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Surface States, Surface Metal-Insulator, and Surface Insulator-Metal TransitionsMay 12 1995I present an informal discussion of various cases where two-dimensional surface metal-insulator structural and charge-density-wave instabilities driven by partly filled surface states have been advocated. These include reconstructions of clean semiconductor ... More

Uniqueness of CP^nAug 23 2015Jun 10 2016We give an exposition of a theorem of Hirzebruch, Kodaira and Yau which proves the uniqueness of the Kahler structure of complex projective space, and of Yau's resolution of the Severi Conjecture.

Connection Between Magnetism and Structure in Fe Double Chains on the Ir(100) SurfaceMar 13 2009The magnetic ground state of nanosized systems such as Fe double chains, recently shown to form in the early stages of Fe deposition on Ir(100), is generally nontrivial. Using ab initio density functional theory we find that the straight ferromagnetic ... More

Third order dielectric susceptibility in a model quantum paraelectricFeb 15 1996In the context of perovskite quantum paraelectrics, we study the effects of a quadrupolar interaction $J_q$, in addition to the standard dipolar one $J_d$. We concentrate here on the nonlinear dielectric response $\chi_{P}^{(3)}$, as the main response ... More

Strain effects at solid surfaces near the melting pointSep 27 2002We investigate the effects of strain on a crystal surface close to the bulk melting temperature T_m, where surface melting usually sets in. Strain lowers the bulk melting point, so that at a fixed temperature below but close to T_m the thickness of the ... More

Triangular Mott-Hubbard Insulator Phases of Sn/Si(111) and Sn/Ge(111) SurfacesMar 07 2007The ground state of Sn/Si(111) and Sn/Ge(111) surface $\alpha$-phases is reexamined theoretically, based on $ab-initio$ calculations where correlations are approximately included through the orbital dependence of the Coulomb interaction (in the local ... More

Ultraviolet and soft X--ray photon--photon elastic scattering in an electron gasJul 17 1993We have considered the processes which lead to elastic scattering between two far ultraviolet or X--ray photons while they propagate inside a solid, modeled as a simple electron gas. The new ingredient, with respect to the standard theory of photon--photon ... More

Path Integral Monte Carlo Study of a Model 2D Quantum ParaelectricJul 17 1993We have begun a study of quantum ferroelectrics and paraelectrics. Simple 2D short-range lattice model hamiltonians are constructed, keeping in mind the phenomenology of real perovskite systems, like $SrTiO_{3}$ and $KTaO_{3}$. Pertinent quantum tunneling ... More

Surface defreezing of glassesDec 14 1999A glass surface may still flow below the bulk glass transition temperature, where the underlying bulk is frozen. Assuming the existence at T=T* of a bulk thermodynamical glass transition, we show that the glass-vapor interface is generally wetted by a ... More

Aftershocks in a frictional earthquake modelMay 12 2016Inspired by spring-block models, we elaborate a "minimal" physical model of earthquakes which reproduces two main empirical seismological laws, the Gutenberg-Richter law and the Omori aftershock law. Our new point is to demonstrate that the simultaneous ... More

Kummer rigidity for K3 surface automorphisms via Ricci-flat metricsAug 27 2018Sep 28 2018We give an alternative proof of a result of Cantat and Dupont, showing that any automorphism of a K3 surface with measure of maximal entropy in the Lebesgue class must be a Kummer example. Our method exploits the existence of Ricci-flat metrics on K3s ... More

The Aleksandrov-Bakelman-Pucci estimate and the Calabi-Yau equationJul 09 2016We give two applications of the Aleksandrov-Bakelman-Pucci estimate to the Calabi-Yau equation on symplectic four-manifolds. The first is solvability of the equation on the Kodaira-Thurston manifold for certain almost-Kahler structures assuming $S^1$-invariance, ... More

The Uneven Distribution of Numbers in NatureAug 27 1998Nov 12 1998Suppose you look at today's stock prices and bet on the value of the first digit. One could guess that a fair bet should correspond to the frequency of $1/9 = 11.11%$ for each digit from 1 to 9. This is by no means the case, and one can easily observe ... More

Can one have preroughening of vicinal surfaces?Oct 27 1999We discuss the possibility that, besides roughening, a vicinal surface could display preroughening (PR), and consider the possible mechanisms for its promotion. Within the framework of a terrace-step-kink model, it turns out that a PR transition is possible, ... More

Monte Carlo studies of quantum and classical annealing on a double-wellDec 03 2005We present results for a variety of Monte Carlo annealing approaches, both classical and quantum, benchmarked against one another for the textbook optimization exercise of a simple one-dimensional double-well. In classical (thermal) annealing, the dependence ... More

Ballistic conductance of magnetic Co and Ni nanowires with ultrasoft pseudo-potentialsMay 19 2004The scattering-based approach for calculating the ballistic conductance of open quantum systems is generalized to deal with magnetic transition metals as described by ultrasoft pseudo-potentials. As an application we present quantum-mechanical conductance ... More

Magnetism in Atomic-Sized Palladium Contacts and NanowiresJul 30 2003We have investigated Pd nanowires theoretically, and found that, unlike either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long, monoatomic wires, we find a spin moment of 0.7 Bohr magnetons per atom, whereas for short, monoatomic ... More

Valley Jahn-Teller effect in twisted bilayer grapheneApr 12 2019The surprising insulating and superconducting states of narrow-band graphene twisted bilayers have been mostly discussed so far in terms of strong electron correlation, with little or no attention to phonons and electron-phonon effects. We found that, ... More

Electron-Stimulated Emission of Na Atoms from NaCl Nanocube CornersFeb 03 2006We performed first principles density functional calculations and simulations of magic-size neutral NaCl nanocubes, and computed the the extraction of a Na neutral corner atom after donating an electron. The atomic structure of the resulting Na corner ... More

Peak Effect versus Skating in High Temperature NanofrictionMar 13 2007The physics of sliding nanofriction at high temperature near the substrate melting point $\Tmelt$ is so far unexplored. We conducted simulations of hard tips sliding on a prototype non-melting surface, NaCl(100), revealing in this regime two distinct ... More

Born Effective Charge Reversal and Metallic Threshold State at a Band Insulator-Mott Insulator TransitionMay 28 1999We study the quantum phase transition between a band (``ionic'') insulator and a Mott-Hubbard insulator, realized at a critical value U=Uc in a bipartite Hubbard model with two inequivalent sites, whose on-site energies differ by an offset Delta. The ... More

The (001) surface of alpha-Ga is covered with GaIIIMar 05 1993We propose, based on ab initio calculations, that the ground state (001) surface of $\alpha$-Ga should be covered by two layers of GaIII, a denser phase which is stable in the bulk only at high pressure and temperature. We discuss how this novel prediction ... More

Premelting of Thin WiresOct 05 1994Recent work has raised considerable interest on the nature of thin metallic wires. We have investigated the melting behavior of thin cylindrical Pb wires with the axis along a (110) direction, using molecular dynamics and a well-tested many-body potential. ... More

Charge density wave surface phase slips and non-contact nanofrictionSep 18 2014Bulk electrical dissipation caused by charge-density-wave (CDW) depinning and sliding is a classic subject. We present a novel local, nanoscale mechanism describing the occurrence of mechanical dissipation peaks in the dynamics of an atomic force microscope ... More

Complex band structure with ultrasoft pseudopotentials: fcc Ni and Ni nanowireFeb 05 2003We generalize to magnetic transition metals the approach proposed by Choi and Ihm for calculating the complex band structure of periodic systems, a key ingredient for future calculations of conductivity of an open quantum system within the Landauer-Buttiker ... More

Selective d-state Conduction Blocking in Nickel NanocontactsNov 20 2001The lowest conductance step for a Ni nanocontact is anomalously small in comparison with the large expected number of conducting channels. We present electronic structure calculations for an extremely idealized Ni nanobridge consisting of just a monatomic ... More

Restricted volumes on Kähler manifoldsAug 25 2016We study numerical restricted volumes of (1,1) classes on compact Kahler manifolds, as introduced by Boucksom. Inspired by work of Ein-Lazarsfeld-Mustata-Nakamaye-Popa on restricted volumes of line bundles on projective manifolds, we pose a natural conjecture ... More

Non-contact dissipation on the surface of charge density wave materialsOct 01 2014Bulk electrical dissipation caused by charge-density-wave (CDW) depinning and sliding is a classic subject. We present a novel local, nanoscale mechanism describing the occurrence of mechanical dissipation peaks in the dynamics of an atomic force microscope ... More

Electron corrected Lorentz forces in solids and molecules in magnetic fieldMar 21 2007We describe the effective Lorentz forces on the ions of a generic insulating system in an magnetic field, in the context of Born-Oppenheimer ab-initio molecular dynamics. The force on each ion includes an important contribution of electronic origin, which ... More

Direct Transition Between a Singlet Mott Insulator and a SuperconductorJan 26 2001May 15 2001We argue that a normal Fermi liquid and a singlet, spin gapped Mott insulator cannot be continuously connected, and that some intermediate phase must intrude between them. By explicitly working out a case study where the singlet insulator is stabilized ... More

Atomic spin sensitive dissipation on magnetic surfacesOct 23 2010We identify the mechanism of energy dissipation relevant to spin-sensitive nanomechanics including the recently introduced magnetic exchange force microscopy, where oscillating magnetic tips approach surface atomic spins. The tip-surface exchange couples ... More

The effect of surface roughness on the adhesion of elastic solidsApr 10 2001We study the influence of surface roughness on the adhesion of elastic solids. Most real surfaces have roughness on many different length scales, and this fact is taken into account in our analysis. We consider in detail the case when the surface roughness ... More

The Puzzling Collapse of Electronic Sliding Friction on a Superconductor SurfaceMay 05 1998In a recent paper [Phys. Rev. Lett. 80 (1998) 1690], Krim and coworkers have observed that the friction force, acting on a thin physisorbed layer of N_2 sliding on a lead film, abruptly decreases by a factor of ~2 when the lead film is cooled below its ... More

Phonons Softening in Tip-Stretched Monatomic NanowiresSep 25 2002It has been shown in recent experiments that electronic transport through a gold monatomic nanowire is dissipative above a threshold voltage due to excitation of phonons via the electron-phonon interaction. We address that data by computing, via density ... More

Islands, craters, and a moving surface step on a hexagonally reconstructed (100) noble metal surfaceJan 14 2000Deposition/removal of metal atoms on the hex reconstructed (100) surface of Au, Pt and Ir should present intriguing aspects, since a new island implies hex -> square deconstruction of the substrate, and a new crater the square -> hex reconstruction of ... More

Spectroscopic fingerprints of a surface Mott-Hubbard insulator: the case of SiC(0001)Jun 16 2000We discuss the spectroscopic fingerprints that a surface Mott-Hubbard insulator should show at the intra-atomic level. The test case considered is that of the Si-terminated SiC(0001) sqrt{3}xsqrt{3} surface, which is known experimentally to be insulating. ... More

Quantum annealing of the Traveling Salesman ProblemFeb 12 2004We propose a path-integral Monte Carlo quantum annealing scheme for the symmetric Traveling Salesman Problem, based on a highly constrained Ising-like representation, and we compare its performance against standard thermal Simulated Annealing. The Monte ... More

Enhanced Electron Pairing in a Lattice of Berry Phase MoleculesJul 19 1994We show that electron hopping in a lattice of molecules possessing a Berry phase naturally leads to pairing. Our building block is a simple molecular site model inspired by C$_{60}$, but realized in closer similarity with Na$_3$. In the resulting model ... More

Optimization by Quantum Annealing: Lessons from Simple CasesFeb 04 2005Feb 10 2005This paper investigates the basic behavior and performance of simulated quantum annealing (QA) in comparison with classical annealing (CA). Three simple one dimensional case study systems are considered, namely a parabolic well, a double well, and a curved ... More

Ballistic Conductance and Magnetism in Short Tip-Suspended Ni NanowiresJan 26 2006Electronic and transport properties of a short Ni nanowire suspended between two semi-infinite ferromagnetic Ni leads are explored in the framework of density-functional theory. The spin-dependent ballistic conductance of the nanowire is calculated using ... More

Ballistic conductance of Ni nanowire with a magnetization reversalOct 15 2003The approach proposed by Choi and Ihm for calculating the ballistic conductance of open quantum systems is generalized to deal with magnetic transition metals. The method has been implemented with ultrasoft pseudopotentials and plane wave basis set in ... More

Valley Jahn-Teller effect in twisted bilayer grapheneApr 12 2019Apr 16 2019The surprising insulating and superconducting states of narrow-band graphene twisted bilayers have been mostly discussed so far in terms of strong electron correlation, with little or no attention to phonons and electron-phonon effects. We found that, ... More

Optimal Energy Dissipation in Sliding Friction SimulationsAug 28 2012Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the removal of the frictionally generated Joule heat. Building upon general pre-existing formulation, we implement ... More

Two-level Physics in a Model Metallic Break JunctionJul 31 2008We consider a model inspired by a metal break-junction hypothetically caught at its breaking point, where the non-adiabatic center-of-mass motion of the bridging atom can be treated as a two-level system. By means of Numerical Renormalization Group (NRG) ... More

Nonlinear hysteretic behavior of a confined sliding layerApr 24 2008A nonlinear model representing the tribological problem of a thin solid lubricant layer between two sliding periodic surfaces is used to analyze the phenomenon of hysteresis at pinning/depinning around a moving state rather than around a statically pinned ... More

Dynamical chiral symmetry breaking in sliding nanotubesMar 09 2009We discovered in simulations of sliding coaxial nanotubes an unanticipated example of dynamical symmetry breaking taking place at the nanoscale. While both nanotubes are perfectly left-right symmetric and nonchiral, a nonzero angular momentum of phonon ... More

Physics and Nanofriction of Alkali Halide Solid Surfaces at the Melting PointFeb 03 2006Feb 08 2006Alkali halide (100) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(100) within a simple (BMHFT) model potential. Calculations of the solid-vapor, solid-liquid and liquid-vapor free energies ... More

Realistic simulations of Au(100): Grand Canonical Monte Carlo and Molecular DynamicsJan 19 2000The large surface density changes associated with the (100) noble metals surface hex-reconstruction suggest the use of non-particle conserving simulation methods. We present an example of a surface Grand Canonical Monte Carlo applied to the transformation ... More

Reentrant layering in rare gas adsorption: preroughening or premelting?Jan 10 2000The reentrant layering transitions found in rare gas adsorption on solid substrates have conflictually been explained either in terms of preroughening (PR), or of top layer melting-solidification phenomena. We obtain adsorption isotherms of Lennard-Jones ... More

Theory of the Metal-Paramagnetic Mott-Jahn-Teller Insulator Transition in A_4C_{60}May 12 1999We study the unconventional insulating state in A_4C_{60} with a variety of approaches, including density functional calculations and dynamical mean-field theory. While the former predicts a metallic state, in disagreement with experiment, the latter ... More

Sealing is at the Origin of Rubber Slipping on Wet RoadsDec 02 2004Loss of braking power and rubber skidding on a wet road is still an open physics problem, since neither the hydrodynamical effects nor the loss of surface adhesion that are sometimes blamed really manage to explain the 20-30% observed loss of low speed ... More

Dynamical Jahn-Teller Effect and Berry Phase in Positively Charged Fullerene I. Basic ConsiderationsSep 19 1995We study the Jahn-Teller effect of positive fullerene ions $^2$C$_{60}^{+}$ and $^1$C$_{60}^{2+}$. The aim is to discover if this case, in analogy with the negative ion, possesses a Berry phase or not, and what are the consequences on dynamical Jahn-Teller ... More

Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half FillingJun 25 2004We propose that electron doped nontransition metal-phthalocyanines (MPc) like ZnPc and MgPc, similar to those very recently reported, should constitute novel strongly correlated metals. Due to orbital degeneracy, Jahn-Teller coupling and Hund's rule exchange, ... More

Kondo impurities in nanotubes: the importance of being "in"Jan 16 2012Transition metal impurities will yield zero bias anomalies in the conductance of well contacted metallic carbon nanotubes, but Kondo temperatures and geometry dependences have not been anticipated so far. Applying the density functional plus numerical ... More

Melting and nonmelting of solid surfaces and nanosystemsApr 26 2005Aug 03 2005We present an extensive but concise review of our present understanding, largely based on theory and simulation work from our group, on the equilibrium behavior of solid surfaces and nanosystems close to the bulk melting point. In the first part we define ... More

Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?Aug 17 2005Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted by their own melt at the triple point. We present extensive simulations for NaCl, followed by calculations of the solid-vapor, solid-liquid, and liquid-vapor free energies showing ... More

Modeling the Unconventional Superconducting Properties of Expanded A$_3$C$_{60}$ FulleridesSep 04 2008The trivalent alkali fullerides A$_3$C$_{60}$, where C$_{60}$ are a well established family of molecular superconductors. The electron pairing has s-wave symmetry and is due to standard electron-phonon coupling, in particular by Jahn-Teller intramolecular ... More

Strongly Correlated Superconductivity and Pseudogap Phase near a multi-band Mott InsulatorJan 07 2004Jul 22 2004Near a Mott transition, strong electron correlations may enhance Cooper pairing. This is demonstrated in the Dynamical Mean Field Theory solution of a twofold-orbital degenerate Hubbard model with inverted Hund's rules on-site exchange, which favors local ... More

Ferroelectricity and isotope effects in hydrogen-bonded KDP crystalsJun 03 2002Based on an accurate first principles description of the energetics in H-bonded KDP, we conduct a first study of nuclear quantum effects and of the changes brought about by deuteration. Cluster tunneling involving also heavy ions is allowed, the main ... More

The NaCl(100) Surface: Why Does it Not Melt?Nov 19 2005The high temperature surface properties of alkali halide crystals are very unusual. Through molecular dynamics simulations based on Tosi-Fumi potentials, we predict that crystalline NaCl(100) should remain stable without any precursor signals of melting ... More

Theoretical Fluctuations of Conductance in Stretched Monatomic NanowireAug 26 2003Recent experiments showed that the last, single channel conductance step in monatomic gold contacts exhibits significant fluctuations as a function of stretching. From simulations of a stretched gold nanowire linked to deformable tips, we determine the ... More

Bending strain-driven modification of surface reconstructions: Au(111)Oct 27 2001Jul 17 2002Strain can affect the morphology of a crystal surface, and cause modifications of its reconstruction even when weak, as in the case of mechanical bending. We carried out calculations of strain-dependent surface free energy and direct bending simulations ... More

Alkali Halide Surfaces Near Melting: Wetting and Nanofriction PropertiesJun 27 2007Alkali halide (100) crystal surfaces are poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(100) within the well tested BMHFT model potential. Calculations of the solid-vapor, solid-liquid and liquid-vapor free energies ... More

Spin gap in low-dimensional Mott insulators with orbital degeneracySep 01 1998We consider the exchange Hamiltonian H_ST = -J Sum_{<rr'>} (2 S_r S_r' - 1/2) (2 T_r T_r' - 1/2) describing two isotropic spin-1/2 Heisenberg antiferromagnets coupled by a quartic term on equivalent bonds. The model is relevant for systems with orbital ... More

Squeezout phenomena and boundary layer formation of a model ionic liquid under confinement and chargingDec 22 2014Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. That includes even-odd switching of the structural layering and ... More

Rubber friction on wet and dry road surfaces: the sealing effectFeb 21 2005Rubber friction on wet rough substrates at low velocities is typically 20-30% smaller than for the corresponding dry surfaces. We show that this cannot be due to hydrodynamics and propose a novel explanation based on a sealing effect exerted by rubber ... More

Electronic friction and liquid-flow-induced voltage in nanotubesJul 12 2004A recent exciting experiment by Ghosh et al. reported that the flow of an ion-containing liquid such as water through bundles of single-walled carbon nanotubes induces a voltage in the nanotubes that grows logarithmically with the flow velocity v0. We ... More

Interaction of a CO molecule with a Pt monoatomic chain: the top geometrySep 03 2008Recent experiments showed that the conductance of Pt nanocontacts and nanowires is measurably reduced by adsorption of CO. We present DFT calculations of the electronic structure and ballistic conductance of a Pt monoatomic chain and a CO molecule adsorbed ... More

Kondo effect of magnetic impurities on nanotubesJan 16 2012The effect of magnetic impurities on the ballistic conductance of nanocontacts is, as suggested in recent work, amenable to ab initio study \cite{naturemat}. Our method proceeds via a conventional density functional calculation of spin and symmetry dependent ... More

Interaction of a CO molecule with a Pt monatomic wire: electronic structure and ballistic conductanceSep 03 2008Sep 04 2008We carry out a first-principles density functional study of the interaction between a monatomic Pt wire and a CO molecule, comparing the energy of different adsorption configurations (bridge, on top, substitutional, and tilted bridge) and discussing the ... More

Physics of Solid and Liquid Alkali Halide Surfaces Near the Melting PointDec 13 2005This paper presents a broad theoretical and simulation study of the high temperature behavior of crystalline alkali halide surfaces typified by NaCl(100), of the liquid NaCl surface near freezing, and of the very unusual partial wetting of the solid surface ... More

Surface molecular dynamics simulation with two orthogonal surface steps: how to beat the particle conservation problemOct 25 2000Due to particle conservation, Canonical Molecular Dynamics (MD) simulations fail in the description of surface phase transitions involving coverage or lateral density changes. However, a step on the surface can act effectively as a source or a sink of ... More

Collective spin 1 singlet phase in high pressure oxygenSep 17 2014Oxygen, one of the most common and important elements in nature, has an exceedingly well explored phase diagram under pressure, up and beyond 100 GPa. At low temperatures, the low pressures antiferromagnetic phases below 8 GPa where O$_2$ molecules have ... More

Strongly Correlated SuperconductivityJul 02 2002High temperature superconductivity in doped Mott insulators such as the cuprates contradicts the conventional wisdom that electron repulsion is detrimental to superconductivity. Because doped fullerene conductors are also strongly correlated, the recent ... More

Sensitivity of the Mott Transition to Non-cubic Splitting of the Orbital Degeneracy: Application to NH3 K3C60Jan 14 2002Mar 22 2002Within dynamical mean-field theory, we study the metal-insulator transition of a twofold orbitally degenerate Hubbard model as a function of a splitting \Delta of the degeneracy. The phase diagram in the U-\Delta plane exhibits two-band and one-band metals, ... More

Spin liquid ground state in a two dimensional non-frustrated spin modelFeb 09 1999We consider an exchange model describing two isotropic spin-1/2 Heisenberg antiferromagnets coupled by a quartic term on the square lattice. The model is relevant for systems with orbital degeneracy and strong electron-vibron coupling in the large Hubbard ... More

High-pressure lubricity at the meso- and nanoscaleJan 11 2013The increase of sliding friction upon increasing load is a classic in the macroscopic world. Here we discuss the possibility that friction rise might sometimes turn into a drop when, at the mesoscale and nanoscale, a confined lubricant film separating ... More

Parameter-free dissipation in simulated sliding frictionAug 06 2010Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the way Joule heat is removed. We implement in a realistic frictional simulation a parameter-free, non-markovian, ... More

Velocity plateaus and jumps in carbon nanotube slidingJul 05 2007The friction between concentric carbon nanotubes sliding one inside the other has been widely studied and simulated, but not so far using external force as the driving variable. Our molecular dynamics (MD) simulations show that as the pulling force grows, ... More

Disordered Flat Phase and Phase Diagram for Restricted Solid on Solid Models of Fcc(110) SurfacesDec 19 1995We discuss the results of a study of restricted solid-on-solid models for fcc (110) surfaces. These models are simple modifications of the exactly solvable BCSOS model, and are able to describe a $(2\times 1)$ missing-row reconstructed surface as well ... More

Calculating Thermodynamics Properties of Quantum Systems by a non-Markovian Monte Carlo ProcedureApr 07 2009We present a history-dependent Monte Carlo scheme for the efficient calculation of the free-energy of quantum systems, inspired by the Wang-Landau sampling and metadynamics method. When embedded in a path integral formulation, it is of general applicability ... More

Metallic charge density waves and surface Mott insulators for adlayer structures on semiconductors: extended Hubbard modelingFeb 02 1998Motivated by the recent experimental evidence of commensurate surface CDW in Pb/Ge(111) and Sn/Ge(111) $\sqrt{3}$-adlayer structures, as well as by the insulating states found on K/Si(111):B and SiC(0001), we have investigated the role of electron-electron ... More

Sliding Over a Phase TransitionMay 24 2011The effects of a displacive structural phase transition on sliding friction are in principle accessible to nanoscale tools such as the Atomic Force Microscopy, yet they are still surprisingly unexplored. We present model simulations demonstrating and ... More

Bent surface free energy differences from simulationNov 28 2000We present a calculation of the change of free energy of a solid surface upon bending of the solid. It is based on extracting the surface stress through a molecular dynamics simulation of a bent slab by using a generalized stress theorem formula, and ... More

Theory of Quantum Annealing of an Ising Spin GlassMay 14 2002Probing the lowest energy configuration of a complex system by quantum annealing was recently found to be more effective than its classical, thermal counterpart. Comparing classical and quantum Monte Carlo annealing protocols on the random two-dimensional ... More

Atomic and electronic structure of ideal and reconstructed $α$-Sn (111) surfaceDec 07 1995We have carried out an ab-initio study of $\alpha$-Sn (111), with the aim of predicting and understanding its structure, reconstructions, and electronic states. We consider a variety of structural possibilities, and optimize them by moving atoms according ... More

On the Critical Points of the E_k Functionals in Kahler GeometryJun 01 2005Oct 02 2006We prove that a Kahler metric in the anticanonical class which is a critical point of the functional E_k and has nonnegative Ricci curvature, is necessarily Kahler-Einstein. This partially answers a question of X.X.Chen.

A general Schwarz Lemma for almost-Hermitian manifoldsJul 04 2007Sep 19 2007We prove a version of Yau's Schwarz Lemma for general almost-complex manifolds equipped with Hermitian metrics. This requires an extension to this setting of the Laplacian comparison theorem. As an application we show that the product of two almost-complex ... More

Limits of Calabi-Yau metrics when the Kahler class degeneratesOct 25 2007Apr 13 2009We study the behaviour of families of Ricci-flat Kahler metrics on a projective Calabi-Yau manifold when the Kahler classes degenerate to the boundary of the ample cone. We prove that if the limit class is big and nef the Ricci-flat metrics converge smoothly ... More

Adiabatic limits of Ricci-flat Kahler metricsMay 28 2009Oct 23 2009We study adiabatic limits of Ricci-flat Kahler metrics on a Calabi-Yau manifold which is the total space of a holomorphic fibration when the volume of the fibers goes to zero. By establishing some new a priori estimates for the relevant complex Monge-Ampere ... More

The Calabi-Yau Theorem and Kähler currentsMay 08 2015Aug 18 2016In this note we give an overview of some applications of the Calabi-Yau theorem to the construction of singular positive (1,1) currents on compact complex manifolds. We show how recent developments allow us to give streamlined proofs of existing results, ... More

Non-Kähler Calabi-Yau manifoldsJan 20 2014Nov 25 2015We study the class of compact complex manifolds whose first Chern class vanishes in the Bott-Chern cohomology. This class includes all manifolds with torsion canonical bundle, but it is strictly larger. After making some elementary remarks, we show that ... More

Calabi-Yau manifolds and their degenerationsSep 03 2011Nov 16 2011This is a short expository note about Calabi-Yau manifolds and degenerations of their Ricci-flat metrics.

The K-energy on small deformations of constant scalar curvature Kahler manifoldsOct 09 2010In this note we give a simplified proof of a recent result of X.X. Chen, which together with work of G. Szekelyhidi implies that on a sufficiently small deformation of a polarized constant scalar curvature Kahler manifold the K-energy has a lower bound. ... More

Kahler-Einstein metrics on Fano surfacesOct 07 2010Oct 09 2010In these notes we give an exposition of a result of G. Tian, which says that a Fano surfaces admits a Kahler-Einstein metric precisely when the Lie algebra of holomorphic vector fields is reductive.

KAWA lecture notes on the Kähler-Ricci flowAug 19 2015May 17 2016These lecture notes are based on a mini-course given by the author at the sixth KAWA Winter School on March 23-26, 2015 at the Centro De Giorgi of Scuola Normale Superiore in Pisa. They provide an introduction to the study of the Kahler-Ricci flow on ... More

Nakamaye's theorem on complex manifoldsMar 01 2016Aug 18 2016We discuss Nakamaye's Theorem and its recent extension to compact complex manifolds, together with some applications.

Degenerations of Calabi-Yau metricsOct 07 2010Oct 14 2010This is a survey of our recent work on degenerations of Ricci-flat Kahler metrics on compact Calabi-Yau manifolds with Kahler classes approaching the boundary of the Kahler cone.

Kahler-Ricci flow on stable Fano manifoldsOct 10 2008We study the Kahler-Ricci flow on Fano manifolds. We show that if the curvature is bounded along the flow and if the manifold is K-polystable and asymptotically Chow semistable, then the flow converges exponentially fast to a Kahler-Einstein metric.

Orthogonality of divisorial Zariski decompositions for classes with volume zeroJun 16 2016We show that the orthogonality conjecture for divisorial Zariski decompositions on compact Kahler manifolds holds for pseudoeffective (1,1) classes with volume zero.