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The performance of five different density functionals (LDA, PBE, PBESOL, B3LYP and PBE0) in describing the infrared spectrum of a crystalline periodic system with a large unit cell (spessartine, 80 atoms in the primitive cell) is studied by using the periodic ab initio C rystal 09 code and an all electron basis set. The transverse (TO) and longitudinal (LO) optical branches of the 17 IR active modes are evaluated together with the oscillator strengths and the high frequency dielectric tensor ϵ ∞ . These ingredients permit to compute the dielectric function ϵ ( ν ) , and then the reflectance spectrum R ( ν ) , which is compared with experiment.

The harmonic frequency spectrum of bulk Mg(OH)(2), brucite, has been computed with the CRYSTAL periodic code, using four different hamiltonians, namely Hartree-Fock (HF), local density (LDA), gradient corrected PW91 and hybrid B3LYP. The anharmonicity of the 011 stretching frequency has also been evaluated, as well as the transverse/longitudinal optical (TO/LO) splitting. Comparison with the frequencies of the single layer shows that the bulk OH stretching splitting is due to interlayer interaction. Agreement with experiment is excellent for B3LYP (less than 10 cm(-1) differences), less so for PW91 and much less satisfactory for both LDA and HF. (C) 2004 Elsevier B.V. All rights reserved

The structural equilibrium parameters, the formation and hydration energies, and the O–H vibrational frequencies of LiOH and NaOH have been investigated at the ab initio level by using the periodic C rystal package. Four different methods have been adopted for comparison. The computed structural parameters are in good agreement with experiment. Computational results are all in excellent agreement with experiment, except for the heat of hydration of LiOH, which was found to be overestimated with respect to experiment. The OH group in the two cases does not present any hydrogen bond type interaction. Among the four methods, B3LYP gives the best results for all the features considered, in particular for the OH(D) vibrational data.

The structural, electronic and elastic properties, as well as the IR and Raman central zone phonon frequencies of CaF 2 , SrF 2 and BaF 2 , have been evaluated by using the periodic ab initio linear combination of atomic orbitals method implemented in the CRYSTAL package. The Hartree–Fock and different density functionals, namely the local density (LDA) and the generalized gradient (GGA), as well as the hybrid B3LYP, Hamiltonians, have been used. The binding energy, equilibrium lattice parameter, elastic constants ( C ij ) and central zone phonon frequencies exhibit a regular and consistent trend in the series, in good agreement with experimental data.

Results are reported on the geometry optimisation of periodic systems with the Hartree–Fock analytical gradients recently implemented in the C rystal code. Application to the structure optimisation of molecules, polymers, slabs and crystals is presented.

The V OH trapped-electron-hole center in magnesium oxide is studied with the periodic ab initio Hartree–Fock program crystal by using the supercell scheme. The H atom that formally is substituted for a Mg atom at its lattice position migrates towards one of the neighboring O atoms, forming a strong covalent bond with it, whereas the hole localizes at the opposite O atom completely. The electronic structure of the defect is discussed in terms of electron charge and spin density maps and band structure. The isotropic and anisotropic components of the hyperfine coupling constant between the H nucleus and the unpaired electron are calculated and are in quite good agreement with ENDOR results.

Silico-faujasite (144 atoms in the unit cell) has been investigated using an ab initio periodic Hartree-Fock scheme and an all-electron basis set. The structure has been fully optimized; it turns out that this system is less stable than α-quartz by about 4 kcal mol−1 per SiO2 unit. The electron density and electrostatic potential maps are used for discussing the differences between pores limited by 6- and 12-membered rings in faujasite.

A finite MgO cluster embedded in the electrostatic field generated by the distributed point multipoles of the perfect crystals is used to evaluate the energy, geometry and charge distribution modifications due to the substitution of the central Mg 2+ ion with a Ca 2+ or Be 2+ ion, using Hartree—Fock theory. Results are compared with well converged periodic supercell data; the three kinds of calculations, namely cluster, perfect periodic crystal and periodic supercell, have been performed with the same program, CRYSTAL, with the same basis set and using similar computational conditions. Good agreement is obtained between the cluster and supercell results when a large cluster is considered. A key condition for such agreement is the homogeneous treatment of the infinite perfect crystal and the cluster.

The electronic structure of crystalline silver chloride has been studied with the ab initio Hartree—Fock program CRYSTAL. Pseudopotentials have been used for describing core electrons. The total energy versus lattice parameter curve was calculated in order to optimize the equilibrium geometry and for evaluating the bulk modulus. A posteriori correlation corrections to the HF energy curve based on density functional schemes bring the calculated binding energy, equilibrium lattice parameter and bulk modulus into reasonable agreement with the experimental data, the percentage errors being around + 5%, +1% and +22% for the three properties, respectively. The electronic structure is investigated with the aid of density of states, band structure and charge-density maps. The strongly but not fully ionic character of AgCl and the importance of correlation effects are confirmed by the present study.

Point group transformation of the LCAO CO basis functions is applied to confine the Roothaan equations within the irreducible part of the Brillouin zone. The general treatment is then translated into the CNDO scheme and a preliminary application to the graphite monolayer is considered.

The electronic structure of corundum (α-Al 2 O 3 ) is calculated at the ab initio Hartree-Fock level. Cohesive energy, total and projected densities of states, atomic multipoles, bond populations and electron charge density distribution maps are given. The oxygen-aluminium bond is found to be partially covalent in nature; the atomic charges are −0.73 e and +1.09 e for O and Al respectively.

Substrate relaxation is shown to play an important role in the 1 : 2 regular chemisorption of hydrogen atoms above alternate carbon atoms in a graphite monolayer. Binding energy, population analysis and electron density maps show that the direct HC bond is strengthened on relaxation.