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Generalized Gradient Approximation (generalized + gradient_approximation)
Selected AbstractsChemical surface passivation of 3C-SiC nanocrystals: A first-principle studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2010A. Trejo Abstract The effect of the chemical surface passivation, with hydrogen atoms, on the energy band gap of porous cubic silicon carbide (PSiC) was investigated. The pores are modeled by means of the supercell technique, in which columns of Si and/or C atoms are removed along the [001] direction. Within this supercell model, morphology effects can be analyzed in detail. The electronic band structure is performed using the density functional theory based on the generalized gradient approximation. Two types of pores are studied: C-rich and Si-rich pores surface. The enlargement of energy band gap is greater in the C-rich than Si-rich pores surface. This supercell model emphasizes the interconnection between 3C-SiC nanocrystals, delocalizing the electronic states. However, the results show a clear quantum confinement signature, which is contrasted with that of nanowire systems. The calculation shows a significant response to changes in surface passivation with hydrogen. The chemical tuning of the band gap opens the possibility plenty applications in nanotechnology. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2455,2461, 2010 [source] Adjusting magnetic moments of Sc13 and Y13 clusters by doping different X atom (X = Na, Mg, Al, Si, P)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2010Fu-Yang Tian Abstract We have investigated the structural and magnetic properties of the doped XM12 and charged M13 (X = Na, Mg, Al, Si, P; M = Sc, Y) clusters using the density-functional theory with spin-polarized generalized gradient approximation. It was found that doped atoms can induce significant change of the magnetic moments of Sc13 and Y13 clusters. The total magnetic moments of the NaM12, MgM12, AlM12, SiM12, and PM12 clusters are regular 5, 6 (12), 7, 8, and 9 ,b, respectively (but 19 ,b for Sc13 and Y13, 12 ,b for Y, 18 ,b for Sc, Sc, and Y). The doped atom substituting the surface atom of the plausible icosahedral configuration is viewed as the ground-state structure of the XM12 (X = Na, P; M = Sc, Y) and MgSc12 clusters. While for XM12 (X = Al, Si; M = Sc, Y) and MgY12 clusters, the doped atom occupying the central position of the icosahedral configuration is viewed as the ground-state structure. The doping and the charging both enhance the stability of the Sc13 and Y13 clusters. These findings should have an important impact on the design of the adjustable magnetic moments systems. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Comparative study of unscreened and screened molecular static linear polarizability in the Hartree,Fock, hybrid-density functional, and density functional modelsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2008Rajendra R. Zope Abstract The sum-over-states (SOS) polarizabilities are calculated within approximate mean-field electron theories such as the Hartree,Fock approximation and density functional models using the eigenvalues and orbitals obtained from the self-consistent solution of the single-particle equations. The SOS polarizabilities are then compared with those calculated using the finite-field (FF) method. Three widely used mean-field models are as follows: (1) the Hartree,Fock (HF) method, (2) the three parameter hybrid generalized gradient approximation (GGA) (B3LYP), and (3) the parameter-free generalized gradient approximation due to Perdew,Burke,Ernzerhof (PBE). The comparison is carried out for polarizabilities of 142 molecules calculated using the 6-311++G(d,p) basis set at the geometries optimized at the B3LYP/6-311G** level. The results show that the SOS method almost always overestimates the FF polarizabilities in the PBE and B3LYP models. This trend is reversed in the HF method. A few exceptions to these trends are found. The mean absolute errors (MAE) in the screened (FF) and unscreened (SOS) polarizability are 0.78, 1.87, and 3.44 Å3 for the HF, B3LYP, and PBE-GGA methods, respectively. Finally, a simple scheme is devised to obtain FF quality polarizability from the SOS polarizability. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] First principles study of small palladium cluster growth and isomerizationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 7 2007Chen Luo Abstract Structures and physical properties of small palladium clusters Pdn up to n = 15 and several selected larger clusters were studied using density functional theory under the generalized gradient approximation. It was found that small Pdn clusters begin to grow 3-dimensionally at n = 4 and evolve into symmetric geometric configurations, such as icosahedral and fcc -like, near n = 15. Several isomers with nearly degenerate average binding energies were found to coexist and the physical properties of these clusters were calculated. For several selected isomers, relatively moderate energy barriers for structural interchange for a given cluster size were found, implying that isomerization could readily occur under ambient conditions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Link between the kinetic- and exchange-energy functionals in the generalized gradient approximationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2002Fabien Tran Abstract An approximate kinetic-energy functional of the generalized gradient approximation form was derived following the "conjointness conjecture" of Lee, Lee, and Parr. The functional shares the analytical form of its gradient dependency with the exchange-energy functionals of Becke and Perdew, Burke, and Ernzerhof. The two free parameters of this functional were determined using the exact values of the kinetic energy of He and Xe atoms. A set of 12 closed-shell atoms was used to test the accuracy of the proposed functional and more than 30 others taken from the literature. It is shown that the conjointness conjecture leads to a very good class of kinetic-energy functionals. Moreover, the functional developed in this work is shown to be one of the most accurate despite its simple analytical form. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Comparison of some representative density functional theory and wave function theory methods for the studies of amino acidsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2009Wenbo Yu Abstract Energies of different conformers of 22 amino acid molecules and their protonated and deprotonated species were calculated by some density functional theory (DFT; SVWN, B3LYP, B3PW91, MPWB1K, BHandHLYP) and wave function theory (WFT; HF, MP2) methods with the 6-311++G(d,p) basis set to obtain the relative conformer energies, vertical electron detachment energies, deprotonation energies, and proton affinities. Taking the CCSD/6-311++G(d,p) results as the references, the performances of the tested DFT and WFT methods for amino acids with various intramolecular hydrogen bonds were determined. The BHandHLYP method was the best overall performer among the tested DFT methods, and its accuracy was even better than that of the more expensive MP2 method. The computational dependencies of the five DFT methods and the HF and MP2 methods on the basis sets were further examined with the 6-31G(d,p), 6-311++G(d,p), aug-cc-pVDZ, 6-311++G(2df,p), and aug-cc-pVTZ basis sets. The differences between the small and large basis set results have decreased quickly for the hybrid generalized gradient approximation (GGA) methods. The basis set convergence of the MP2 results has been, however, very slow. Considering both the cost and the accuracy, the BHandHLYP functional with the 6-311++G(d,p) basis set is the best choice for the amino acid systems that are rich in hydrogen bonds. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Ab-initio simulations of materials using VASP: Density-functional theory and beyondJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Jürgen Hafner Abstract During the past decade, computer simulations based on a quantum-mechanical description of the interactions between electrons and between electrons and atomic nuclei have developed an increasingly important impact on solid-state physics and chemistry and on materials science,promoting not only a deeper understanding, but also the possibility to contribute significantly to materials design for future technologies. This development is based on two important columns: (i) The improved description of electronic many-body effects within density-functional theory (DFT) and the upcoming post-DFT methods. (ii) The implementation of the new functionals and many-body techniques within highly efficient, stable, and versatile computer codes, which allow to exploit the potential of modern computer architectures. In this review, I discuss the implementation of various DFT functionals [local-density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, hybrid functional mixing DFT, and exact (Hartree-Fock) exchange] and post-DFT approaches [DFT + U for strong electronic correlations in narrow bands, many-body perturbation theory (GW) for quasiparticle spectra, dynamical correlation effects via the adiabatic-connection fluctuation-dissipation theorem (AC-FDT)] in the Vienna ab initio simulation package VASP. VASP is a plane-wave all-electron code using the projector-augmented wave method to describe the electron-core interaction. The code uses fast iterative techniques for the diagonalization of the DFT Hamiltonian and allows to perform total-energy calculations and structural optimizations for systems with thousands of atoms and ab initio molecular dynamics simulations for ensembles with a few hundred atoms extending over several tens of ps. Applications in many different areas (structure and phase stability, mechanical and dynamical properties, liquids, glasses and quasicrystals, magnetism and magnetic nanostructures, semiconductors and insulators, surfaces, interfaces and thin films, chemical reactions, and catalysis) are reviewed. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Energy landscapes of nucleophilic substitution reactions: A comparison of density functional theory and coupled cluster methodsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2007Marcel Swart Abstract We have carried out a detailed evaluation of the performance of all classes of density functional theory (DFT) for describing the potential energy surface (PES) of a wide range of nucleophilic substitution (SN2) reactions involving, amongst others, nucleophilic attack at carbon, nitrogen, silicon, and sulfur. In particular, we investigate the ability of the local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA as well as hybrid DFT to reproduce high-level coupled cluster (CCSD(T)) benchmarks that are close to the basis set limit. The most accurate GGA, meta-GGA, and hybrid functionals yield mean absolute deviations of about 2 kcal/mol relative to the coupled cluster data, for reactant complexation, central barriers, overall barriers as well as reaction energies. For the three nonlocal DFT classes, the best functionals are found to be OPBE (GGA), OLAP3 (meta-GGA), and mPBE0KCIS (hybrid DFT). The popular B3LYP functional is not bad but performs significantly worse than the best GGA functionals. Furthermore, we have compared the geometries from several density functionals with the reference CCSD(T) data. The same GGA functionals that perform best for the energies (OPBE, OLYP), also perform best for the geometries with average absolute deviations in bond lengths of 0.06 Å and 0.6°, even better than the best meta-GGA and hybrid functionals. In view of the reduced computational effort of GGAs with respect to meta-GGAs and hybrid functionals, let alone coupled cluster, we recommend the use of accurate GGAs such as OPBE or OLYP for the study of SN2 reactions. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Proton affinities of maingroup-element hydrides and noble gases: Trends across the periodic table, structural effects, and DFT validationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2006Marcel Swart Abstract We have carried out an extensive exploration of the gas-phase basicity of archetypal neutral bases across the periodic system using the generalized gradient approximation (GGA) of the density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. First, we validate DFT as a reliable tool for computing proton affinities and related thermochemical quantities: BP86/QZ4P//BP86/TZ2P is shown to yield a mean absolute deviation of 2.0 kcal/mol for the proton affinity at 298 K with respect to experiment, and 1.2 kcal/mol with high-level ab initio benchmark data. The main purpose of this work is to provide the proton affinities (and corresponding entropies) at 298 K of the neutral bases constituted by all maingroup-element hydrides of groups 15,17 and the noble gases, that is, group 18, and periods 1,6. We have also studied the effect of step-wise methylation of the protophilic center of the second- and third-period bases. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1486,1493, 2006 [source] Newly developed basis sets for density functional calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2005S. Chiodo Abstract Optimized contracted Gaussian basis sets of double-zeta valence polarized (DZVP) quality for first-row transition metals are presented. The DZVP functions were optimized using the PWP86 generalized gradient approximation (GGA) functional and the B3LYP hybrid functional. For a careful analysis of the basis sets performance the transition metal atoms and cations excitation energies were calculated and compared with the experimental ones. The calculated values were also compared with those obtained using the previously available DZVP basis sets developed at the local-density functional level. Because the new basis sets work better than the previous ones, possible reasons of this behavior are analyzed. The newly developed basis sets also provide a good estimation of other atomic properties such as ionization energies. © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 175,183, 2005 [source] Half-metallicity and magnetism at Heusler alloy surfaces: Co2MSi(001) (M = Ti, Cr)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008Ying Jiu Jin Abstract We investigated the electronic structures, magnetism, and half-metallicity at the (001) surfaces of full-Heusler alloys, Co2MSi (M = Ti, Cr), by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. Both the Co-terminated (Co-term) and the MSi-terminated (MSi-term) surfaces were considered. From the calculated atom-resolved density of states, we found that the half-metallicity was destroyed at the Co-term surfaces for both alloys. The electronic structures at the MSi-term surfaces of the two alloys showed much different behavior. The half-metallicity was retained at the TiSi-term for Co2TiSi(001) but the minority spin gap was much reduced due to surface states located just below the Fermi level. On the other hand the half-metallicity was destroyed at the CrSi-term of Co2CrSi(001) due to the surface states located at the Fermi level. The calculated magnetic moment of the surface Co atom of the Co-term for Co2CrSi(001) was increased slightly to 1.05,B with respect to that of the deep inner layers (,1.00,B), while that for Co2TiSi(001) was decreased to 0.88,B. Large enhancement of the magnetic moment was found for the surface Ti atoms at TiSi-term of Co2TiSi(001) and Cr atoms at CrSi-term of Co2CrSi(001) with values of 0.07,B and 2.91(B, respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical spectra of bismuth sulfochloride crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2010A. Audzijonis Abstract We present the results of the ab initio theoretical study of the optical properties for paraelectric BiSCl crystal using the full potential linearized augmented plane wave (FP-LAPW) method as implanted in the Wien 2k code. For theoretical calculations of optical constants and functions we used the generalized gradient approximation (PBE-GGA), an improvement of the local spin-density approximation (LSDA) and recently Wu,Cohen (WC) proposed a new WC-GGA exchange-correlation energy functional. The dielectric function, refractive index, extinction coefficient, absorption coefficient, reflectivity, and energy loss function were calculated. The optical properties are analyzed and the origins of the peaks in the spectra are discussed in terms of the calculated density of states. [source] Simulation of electronic density of states and optical properties of PbB4O7 by first-principles DFT methodPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2009Hui Wang Abstract First-principles calculations based on the density functional theory and the generalized gradient approximation were carried out to systematically investigate the electronic structure and linear optical properties of lead tetraborate (PbB4O7; PTB) single crystals. An indirect band gap of 4.34 eV is obtained. The valence band top is at the X-point and the conduction band is at the ,-point. The calculated total and partial densities of states indicate that the top valence band is constructed from O 2p states and the low conduction band mainly consists of Pb 6p states. The optical absorption spectra show several prominent structures but with very small directional anisotropy. PTB crystals have a higher refractive index but a small birefringence. The calculated frequency-dependent refractive index is in good agreement with experimental data. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phase transition and elasticity of CdO under pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Feng Peng Abstract First-principles calculations of the crystal structures, and phase transition, and elastic properties of cadmium oxide (CdO) have been carried out with the plane-wave pseudopotential within the generalized gradient approximation in the frame of density functional theory method. The calculated values (for crystal structures) are in good agreement with experimental data as well as with some of the existing model calculations. For CsCl-type CdO, the dependence of the elastic constants cij, the aggregate elastic modulus (B, G, E), and the elastic anisotropy on the pressure have been investigated. Moreover, the pressure dependences of the Poisson ratio, Debye temperature, and the compressional and shear elastic wave velocities have been investigated for the first time. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural, electronic and optical properties of lead zirconatePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008J. Baedi Abstract The structure, the band structure, the total density of states, the dielectric function, the extinction coefficient and the refractive index have been calculated for lead zirconate (PbZrO3) using density functional theory (DFT). The full potential linearized augmented plane wave (FL-LAPW) method was used with the generalized gradient approximation (GGA). Calculations of the optical spectra have been performed for the energy range 0,28 eV. It is shown that the orthorhombic PbZrO3, which is optically negative, exhibits a biaxial birefringence and its refractive index is smallest along the a -axis (na (0) = 2.32, nb (0) = 2.36 and nc (0) = 2.34) which is close to the experimental value. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] First-principles study of the structural stability and electronic structures of TaNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008C. L. Cao Abstract Using the plane-wave pseudopotential method within the generalized gradient approximation, we have studied the structural stability and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetic stability of phase structures of TaN from low to high is: CsCl < ZnS-B3 < NaCl < WC < CoSn. The higher stability of TaN in the CoSn and WC structures is due to the formation of pseudogap around the Fermi level and the stronger hybridization between N-2p states and Ta-5d states. TaN in all structures studied has a metallic nature. The calculated bulk modulus indicates that TaN in the WC structure may be a less compressible material. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The electronic structure and magnetism of a rocksalt FeN(001) surface: A density functional studyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007J. I. Lee Abstract We investigated the electronic structure and magnetism of the rocksalt FeN(001) surface. We considered both the ferromagnetic and antiferromagnetic configurations. We calculated the electronic structure using the full-potential linearized augmented plane wave method within generalized gradient approximation. We found that the antiferromagnetic phase is more stable than the ferromagnetic one, as in bulk, with an energy difference of 0.14 eV per the considered slab. The magnetic moments of the Fe atoms in the antiferromagnetic phase slab are 2.90 ,B, ,2.26 ,B and 2.37 ,B for the surface, subsurface, and center layers, respectively, while the values for the ferromagnetic one are 2.85 ,B, 1.81 ,B, and 2.37 ,B, respectively. The detailed electronic structures for ferromagnetic and antiferromagnetic phases are compared and discussed with the calculated spin-densities and density of states. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Band structure and optical properties of SbSeI: density-functional calculationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007Harun Akkus Abstract The electronic structure and linear optical properties of the ferroelectric semiconductor SbSeI are calculated in the nonpolar phase using the density functional methods in the generalized gradient approximation. The obtained electronic band structure shows that SbSeI has an indirect forbidden gap of 1.65 eV. The linear photon-energy-dependent dielectric functions and some optical functions such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity and optical conductivity are calculated. Moreover, some important optical parameters such as the effective number of valence electrons and the effective optical dielectric constant are calculated. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] How do electronic properties of conventional III,V semiconductors hold for the III,V boron bismuth BBi compound?PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2005D. Madouri Abstract We have performed ab-initio self-consistent calculations using the full potential linear augmented plane wave method to investigate the structural and the electronic properties of the boron bismuth III,V compound BBi. Our calculations provide the first available information about the structural and electronic ground-state properties of BBi. Total energy calculations of the cubic zinc-blende, wurtzite, rock-salt, cesium chloride and orthorhombic Cmcm phases are made. The zinc-blende structure is found to be the ground-state phase of BBi; within the generalized gradient approximation (local density approximation), we found a lattice constant of 5.529 Å (5.416 Å) and a bulk modulus of 72.20 GPa (86.27 GPa). We found that, contrary to other boron compounds, the band gap of BBi is direct at the , point. The relativistic contraction of the 6s orbital of Bi has a strong influence on the bands and bonds of BBi. Consequently, the electronic properties of BBi are shown to differ considerably from those of common group III,V semiconductors (e.g. GaAs); in particular, we found an unusually strong p,p mixing of the valence-band maximum relative to most of the other III,V compounds. Furthermore, the calculated valence charge density shows an anomalous behavior, characterized by a charge transfer towards the ,cation' B atom, further illustrating the rich behavior of boron bismuth compounds. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic and structural properties of strontium chalcogenides SrS, SrSe and SrTePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004D. Rached Abstract We present the results of a first-principles study of the electronic and structural properties of strontium chalcogenides, SrS, SrSe and SrTe. The computational method is based on the full-potential linear muffin-tin orbitals method (FP-LMTO) augmented by a plane-wave basis (PLW). The exchange and correlation energy is described in the local density approximation (LDA) using the Perdew,Wang parameterization including a generalized gradient approximation (GGA). The calculated results of the structural properties are given for the NaCl (B1) and CsCl (B2) structures. We have also carried out band-structure calculations for the three considered compound, but only for the NaCl (B1) structure. A reasonable agreement is found from the comparison of our results with other theoretical calculations and experimental data. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] EuI2, a low-temperature europium(II) iodide phaseACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Michael Krings Light-yellow europium(II) diiodide, prepared by the low-temperature reaction of europium and ammonium iodide in liquid ammonia at 200,K and characterized by high-resolution X-ray powder diffraction, represents a new phase for EuI2 that adopts an orthorhombic Pnma structure with all three atoms lying on 4c positions (.m.). It is isotypic with SrI2(IV). Temperature-dependent X-ray measurements performed to investigate the thermal stability of the new phase show that it decomposes irreversibly to amorphous material around 673,K. Total-energy density-functional calculations using the generalized gradient approximation suggest this to be the ground-state structure of EuI2. [source] DFT Study of Effects of Potassium Doping on Band Structure of Crystalline Cuprous AzideCHINESE JOURNAL OF CHEMISTRY, Issue 12 2008Wei-Hua ZHU Abstract The structure and defect formation energies of the K-doped CuN3 were studied using density functional theory within the generalized gradient approximation. The results show that the K-doping breaks the azide symmetry and causes asymmetric atomic displacement. As the K-doping level increases, the band gap of the doped system gradually increases. The K impurity is easily incorporated into the crystal thermodynamically. The Cu vacancy is easily created thermodynamically and the K impurity can serve as nucleation centers for vacancy clustering. Finally the effects of K-doping concentrations on the sensitivity of CuN3 were understood based on electronic structures. [source] Application of standard DFT theory for nonbonded interactions in soft matter: Prototype study of poly- para -phenyleneJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2006Marcelo Alves-Santos Abstract We present a detailed analysis of the application of density functional theory (DFT) methods to the study of structural properties of molecular and supramolecular systems, using as a paradigmatic example three para -phenylene-based systems: isolated biphenyl, single chain poly- para -phenylene, and crystalline biphenyl. We use different functionals for the exchange correlation potential, the local density (LDA), and generalized gradient approximations (GGA), and also different basis sets expansions, localized, plane waves (PW), and mixed (localized plus PW), within the reciprocal space formulation for the hamiltonian. We find that regardless of the choice of basis functions, the GGA calculations yield larger interring distances and torsion angles than LDA. For the same XC approximation, the agreement between calculations with different basis functions lies within 1% (LDA) or 0.5% (GGA) for distances, and while PW and mixed basis calculations agree within 1° for torsion angles, the localized basis results show larger angles by , 8° and a nonmonotonic dependence on basis size, with differences within 6°. The most prominent features, namely the torsion between rings for isolated molecule and infinite chain, and planarity for the molecule in crystalline environment, are well reproduced by all DFT calculations. © 2005 Wiley Periodicals, Inc. J Comput Chem 27: 217,227, 2006 [source] | |||||||||||||