Guo-xu Zhang

Harbin Institute Of Technology, ITSC, Faculty Member

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Van der Waals forces in solids: Challenges for density functionals

While the importance of van der Waals (vdW) forces for binding between molecules is well establis... more While the importance of van der Waals (vdW) forces for binding between molecules is well established, their influence on the cohesive properties of solids remains to be quantified from first-principles. In particular, most state-of-the-art density functionals yield systematic deviations for the lattice constants, cohesive energies, bulk moduli and transition pressures for a range of solid-state systems. We evaluate the long-range C6 dispersion coefficients for ions in solids and use them to assess the effect of the long-range vdW forces on the abovementioned cohesive properties of ionic (NaCl, AgCl, MgO) and semiconductor (Si, GaAs) solids. For all of these systems, we obtain consistently accurate results by coupling the long-range C6R-6 dispersion energy with the Perdew-Burke-Ernzerhof functional for the short range. We compare our results for the cohesive properties with recently developed functionals for solids.

How van der Waals Interactions Influence Cohesive Properties of Non-Metallic Solids

$Research paper thumbnail of \ textit {Atoms in Solids} Perspective on Polarizabilities and van der Waals Coefficients in Semiconductors$

\ textit {Atoms in Solids} Perspective on Polarizabilities and van der Waals Coefficients in Semiconductors

First-principles investigation of stability and structural properties of the BaTiO3 (110) polar surface

The atomic and electronic structures of the BaTiO 3 (110) polar surface were systematically inves... more The atomic and electronic structures of the BaTiO 3 (110) polar surface were systematically investigated by first-principles density functional theory (DFT) calculations with use of slab models. The relaxations and rumplings of five different (1 × 1) terminations were considered. According to the results of the charge redistribution, the polarity compensation conditions can be achieved in both stoichiometric and nonstoichiometric terminations, but their compensation mechanisms are obviously different. For the BaTiO and O 2 stoichiometric terminations, the intensive electronic structure changes with respect to the bulk crystal result in larger structural distortions and cleavage energies than the nonstoichiometric ones. For the TiO, Ba, and O nonstoichiometric terminations, whose electronic structures are qualitatively similar to that of the bulk crystal, their insulating characteristics are retained because no filling of surface states was found. Furthermore, the computation results of the surface grand potentials (SGPs), which were used to distinguish the relative stabilities of different terminations, clearly suggest the existence of four distinct stable (110) terminations, in which the BaTiO stoichiometric termination can only exist in a small region with O-poor condition.

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A first-principles investigation of the stabilities and electronic properties of SrZrO3 (1 1 0) (1 × 1) polar terminations

Journal of physics. Condensed matter : an Institute of Physics journal, 2014

The stabilities and electronic properties of SrZrO3 (1 1 0) (1 × 1) polar terminations were inv... more The stabilities and electronic properties of SrZrO3 (1 1 0) (1 × 1) polar terminations were investigated systematically by the first-principles density functional theory method. Five possible polar surfaces, i.e. O-deficient, O-rich, stoichiometric, SrO-rich and SrO-deficient ones, were considered. The calculated results indicated that the charge neutralization and polarity compensation condition could be achieved by charge redistributions of surface atoms. For the O-deficient (1 1 0) termination, some filled electronic states were separated from the original conduction bands, while a surface reconstruction was found for the O-rich (1 1 0) surface. The remaining three (1 1 0) terminations remained insulated. Furthermore, a stability diagram involving seven different terminations was constructed using the surface grand potential technique, in which the effect of the chemical environment was included. The calculated results indicated that three (1 1 0) (O-rich, SrO-rich and stoichio...

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van der Waals Interactions in Ionic and Semiconductor Solids

by Guo-xu Zhang and Joachim Paier

Physical Review Letters, 2011

van der Waals (vdW) energy corrected density-functional theory [Phys. Rev. Lett. 102, 073005 (200... more van der Waals (vdW) energy corrected density-functional theory [Phys. Rev. Lett. 102, 073005 (2009)] is applied to study the cohesive properties of ionic and semiconductor solids (C, Si, Ge, GaAs, NaCl, and MgO). The required polarizability and dispersion coefficients are calculated using the dielectric function obtained from time-dependent density-functional theory. Coefficients for &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;atoms in the solid&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; are then calculated from the Hirshfeld partitioning of the electron density. It is shown that the Clausius-Mossotti equation that relates the polarizability and the dielectric function is accurate even for covalently-bonded semiconductors. We find an overall improvement in the cohesive properties of Si, Ge, GaAs, NaCl, and MgO, when vdW interactions are included on top of the Perdew-Burke-Ernzerhof or Heyd-Scuseria-Ernzerhof functionals. The relevance of our findings for other solids is discussed.

Electrodynamic response and stability of molecular crystals

by Guo-xu Zhang and Bohdan Schatschneider

Physical Review B, 2013

ABSTRACT We show that electrodynamic dipolar interactions, responsible for long-range fluctuation... more ABSTRACT We show that electrodynamic dipolar interactions, responsible for long-range fluctuations in matter, play a significant role in the stability of molecular crystals. Density functional theory calculations with van der Waals interactions determined from a semilocal &quot;atom-in-a-molecule&quot; model result in a large overestimation of the dielectric constants and sublimation enthalpies for polyacene crystals from naphthalene to pentacene, whereas an accurate treatment of non-local electrodynamic response leads to an agreement with the measured values for both quantities. Our findings suggest that collective response effects play a substantial role not only for optical excitations, but also for cohesive properties of non-covalently bound molecular crystals.

Structure and energetics of benzene adsorbed on transition-metal surfaces: density-functional theory with van der Waals interactions including collective substrate response

New Journal of Physics, 2013

The adsorption of benzene on metal surfaces is an important benchmark system for hybrid inorganic... more The adsorption of benzene on metal surfaces is an important benchmark system for hybrid inorganic/organic interfaces. The reliable determination of the interface geometry and binding energy presents a significant challenge for both theory and experiment. Using the Perdew-Burke-Ernzerhof (PBE), PBE+vdW (van der Waals) and the recently developed PBE+vdW surf (densityfunctional theory with vdW interactions that include the collective electronic response of the substrate) methods, we calculated the structures and energetics for benzene on transition-metal surfaces: Cu, Ag, Au, Pd, Pt, Rh and Ir. Our calculations demonstrate that vdW interactions increase the binding energy by more than 0.70 eV for physisorbed systems (Cu, Ag and Au) and by an even larger amount for strongly bound systems (Pd, Pt, Rh and Ir). The collective response of the substrate electrons captured via the vdW surf method plays a significant role for most substrates, shortening the equilibrium distance by 0.25 Å for Cu and decreasing the binding energy by 0.27 eV for Rh. The reliability of our results is assessed by comparison with calculations using the random-phase approximation including renormalized single excitations,

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Lattice dynamics investigation of different transition behaviors of cubic BaTiO 3 and SrTiO 3 by first-principles calculations

Journal of Physics: Condensed Matter, 2008

... SrTiO3 by first-principles calculations Ying Xie, Hai-tao Yu, Guo-xu Zhang and Hong-gang Fu1 ... more

A first-principles investigation into the ferroelectric and antiferrodistortive instabilities of cubic SrTiO 3

Journal of Physics: Condensed Matter, 2007

ABSTRACT The lattice dynamics and potential energy curves of cubic SrTiO3 as a function of lattic... more ABSTRACT The lattice dynamics and potential energy curves of cubic SrTiO3 as a function of lattice volume were investigated by density functional theory (DFT) calculations. The calculated results indicate that the lowest optical phonon in the Brillouin-zone center is real and an unstable R25 mode, corresponding to the antiferrodistortive transition, is found at the equilibrium volume. The results are consistent with previous experimental predictions. Moreover, increasing volume can improve the ferroelectric instability and restrain the antiferrodistortive one. A competition between the ferroelectric and antiferrodistortive instabilities does exist. The smaller lattice constant of cubic SrTiO3 than of BaTiO3 is crucial both for the appearance of the antiferrodistortive instability and the disappearance of the ferroelectric instability, which makes the transition behaviors of the two compounds entirely different.

First-principles calculations of the stability and electronic properties of the PbTiO 3 (110) polar surface

Journal of Computational Chemistry, 2009

The structural and electronic properties of five terminations of cubic lead titanate (PbTiO 3 ) (... more The structural and electronic properties of five terminations of cubic lead titanate (PbTiO 3 ) (110) polar surface were investigated by first-principles total-energy calculations using a periodic slab model. On the PbTiO termination, an anomalous filling of conduction band was observed, whereas on the O 2 termination, two surface oxygen atoms formed a peroxo group, demonstrating that the electronic structures of the two stoichiometric terminations undergo significant changes with respect to bulk materials. However, for the three nonstoichiometric TiO-, Pb-, and O-terminated surfaces, their electronic structures are very similar to bulk. Charge redistribution results for the five terminations confirmed that electronic structure and surface composition changes are responsible for their polarity compensation. However, which mechanism actually dominates the stabilization process depends upon energetic considerations. A thermodynamic stability diagram suggested that the two stoichiometric terminations are unstable; however, the three nonstoichiometric terminations can be stabilized in some given regions. Furthermore, this study indicates that the very different stabilities and surface states filling behaviors of the PbTiO 3 (110) polar surface with respect to SrTiO 3 and BaTiO 3 ones seem to originate from the partially covalent characteristics of PbÀ ÀO pairs. q

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Van der Waals forces in solids: Challenges for density functionals

A Study of the Catalyst and Synthesis of o-Cresol

Van der Waals interactions in semiconductor solids

by Guo-xu Zhang and Joachim Paier

The binding in semiconductor solids arises mainly from the covalent hybridization of atomic orbit... more The binding in semiconductor solids arises mainly from the covalent hybridization of atomic orbitals. Hence, it is typically assumed that van der Waals (vdW) interactions play a minor role for their cohesion. In order to probe this conventional wisdom we develop a method to calculate accurate long-range vdW coefficients for ions and atoms in crystals. We first assess the validity of the Clausius-Mossotti relation between the polarizability and dielectric function for bulk semiconductors by comparing periodic TDDFT calculations to direct extrapolation of the frequency-dependent TDDFT polarizability for finite clusters. We find a good agreement between these two approaches for computing vdW C6(V) coefficients for a broad variation in the unit cell volume V for diamond, Si, and Ge crystals. When using TDDFT@HSE with the Nanoquanta kernel, the volume-dependent dielectric constant of Si and Ge is in excellent agreement with experimental data. The crystal-field screening reduces the vdW coefficients by a factor of two compared to corresponding free-atom and effective hybridized C6[n(r)] values [1]. The use of accurate C6(V) coefficients in the PBE+vdW method [1] improves cohesive properties of Si and Ge in comparison to experimental data. [1] A. Tkatchenko and M. Scheffler, Phys. Rev. Lett. 102, 073005 (2009).

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