K. Doll

Analytical Hartree–Fock gradients for periodic systems

We present the theory of analytical Hartree–Fock gradients for periodic systems as implemented in the code CRYSTAL. We demonstrate how derivatives of the integrals can be computed with the McMurchie–Davidson algorithm. Highly accurate gradients with respect to nuclear coordinates are obtained for systems periodic in 0, 1, 2, or 3 dimensions.

Implementation of analytical Hartree-Fock gradients for periodic systems

Abstract We describe the implementation of analytical Hartree–Fock gradients for periodic systems in the code CRYSTAL, emphasizing the technical aspects of this task. The code is now capable of calculating analytical derivatives with respect to nuclear coordinates for systems periodic in 0, 1, 2 and 3 dimensions (i.e. molecules, polymers, slabs and solids). Both closed-shell restricted and unrestricted Hartree–Fock gradients have been implemented. A comparison with numerical derivatives shows that the forces are highly accurate.

Ab initio study of the vibrational spectrum and related properties of crystalline compounds; the case of CaCO3 calcite

Abstract The static and high frequency dielectric tensors, Born effective charges, vibrational spectrum at the Γ point, TO-LO splitting and IR intensities of calcite CaCO3 have been calculated with the periodic ab initio CRYSTAL program, with five different basis sets of increasing size and four different Hamiltonians (HF, LDA, PBE, B3LYP). B3LYP is shown to perform better than the other options, in particular of LDA and PBE that are often used for the calculation of the vibrational spectrum of crystalline solids. When comparing B3LYP and experimental frequencies, the mean absolute difference is as small as 8.5 cm-1; this number reduces to 4.8 cm-1 if the two lowest experimental frequencies, that we suspect to be affected by a relatively large error, are excluded from statistics. Static and high frequency dielectric tensors, as well as IR intensities computed with the same hybrid scheme (B3LYP) compare quite favourably with experiment. The full set of modes is characterized by various tools including isotopic substitution, “freezing” one of the two subunits (Ca2+ or CO32-) and graphical representations. A general tool has been implemented, that permits the automatic generation of the animation of the full set of modes starting from the CRYSTAL output (available at www.crystal.unito.it/vibs/calcite).

Chlorine adsorption on the Cu(111) surface

Abstract We investigate the adsorption of chlorine on the Cu(111) surface with full-potential all-electron density functional calculations. Chlorine adsorption at the fcc hollow sites is slightly preferred over that at the hcp hollow. The adsorption geometry is in excellent agreement with electron diffraction and ion scattering data. Adsorption energies and surface diffusion barriers are close to those deduced from experiment.

Performance of six functionals (LDA, PBE, PBESOL, B3LYP, PBE0, and WC1LYP) in the simulation of vibrational and dielectric properties of crystalline compounds. The case of forsterite Mg2SiO4

The performance of six different density functionals (LDA, PBE, PBESOL, B3LYP, PBE0, and WC1LYP) in describing the infrared spectrum of forsterite, a crystalline periodic system with orthorhombic unit cell (28 atoms in the primitive cell, Pbmn space group), is investigated by using the periodic ab initio CRYSTAL09 code and an all‐electron Gaussian‐type basis set. The transverse optical (TO) branches of the 35 IR active modes are evaluated at the equilibrium geometry together with the oscillator strengths and the high‐frequency dielectric tensor ϵ∞. These quantities are essential to compute the dielectric function ϵ(ν), and then the reflectance spectrum R(ν), which is compared with experiment. It turns out that hybrid functionals perform better than LDA and GGA, in general; that B3LYP overperforms WC1LYP and, in turn, PBE0; that PBESOL is better than PBE; that LDA is the worst performing functional among the six under study.

A density functional study of lithium bulk and surfaces

We report the bulk and surface properties of lithium computed within a full-potential linear combination of Gaussian-type orbitals formalism using both density functional theory and the Hartree-Fock approximation. We examine the convergence of computed properties with respect to numerical approximations and also explore the use of finite-temperature density functional theory. We demonstrate that fully converged calculations reproduce cohesive properties, elastic constants, band structure, and surface energies in full agreement with experimental data and, where available, previous calculations.

Correlation effects in ionic crystals: The cohesive energy of MgO

High-level quantum-chemical calculations, using the coupled-cluster approach and extended one-particle basis sets, have been performed for (Mg2+)n (O2-)m clusters embedded in a Madelung potential. The results of these calculations are used for setting up an incremental expansion for the correlation energy of bulk MgO. This way, 96% of the experimental cohesive energy of the MgO crystal is recovered. It is shown that only 60% of the correlation contribution to the cohesive energy is of intra-ionic origin, the remaining part being caused by van der Waals-like inter-ionic excitations.

Closed-shell interaction in silver and gold chlorides

Hartree–Fock and coupled-cluster calculations have been performed for cubic AgCl and for AuCl having a cubic or the observed structure with space group I41/amd. Cohesive energies and lattice constants are in excellent agreement with experiment for AgCl; for AuCl we find good agreement, and the experimental structure is correctly predicted to be lower in energy than the cubic one. Electron-correlation effects on lattice constants are very large, of up to 0.8 A for cubic AuCl. We especially discuss the strength of the closed-shell interactions, and for the first time a quantitative analysis of the so-called “aurophilic” Au(I)–Au(I) interaction is presented in solids.

Quantum chemical approach to cohesive properties of NiO

We apply ab-initio quantum chemical methods to calculate correlation effects on cohesive properties of NiO, thereby extending a recently proposed scheme to transition metal oxides with partially filled

Correlation effects in MgO and CaO: Cohesive energies and lattice constants

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