Structural, vibrational and electronic properties of a crystalline hydrate from ab initio periodic Hartree–Fock calculations

Abstract

The hydrate crystal lithium hydroxide monohydrate LiOH.H20 has been studied by ab initio periodic Hartree-Fock calculations. The influence of the crystalline environment on the local molecular properties (molecular geometry, atomic charges, electron density, molecular vibrations and deuterium quadrupole coupling constants) of the water molecule, the lithium and hydroxide ions has been calculated. A number of crystalline bulk properties are also presented; optimized crystalline structure, lattice energy and electronic band structure. The optimized cell parameters from calculations with a large basis set of triple-zeta quality differ by only 1-3% from the experimental neutron-determined cell, whereas the STO-3g basis set performs poorly (differences of 5-10%). With the triple-zeta basis also the atomic positions and intermolecular distances agree very well with the experiment. The lattice energy differs by -8% from the experimental value, and by at most 3% when a density-functional electron correlation correction is applied. Large electron-density rearrangements occur in the water molecule and in the hydrogen bond and are in qualitative and quanti-© 1994 International Union of Crystallography Printed in Great Britain -all rights reserved tative agreement with experimental X-ray diffraction results. The quadrupole-coupling constants of the water and hydroxide deuterium atoms are found to be very sensitive to the O---H bond length and are in good agreement with experimental values when the calculation is based on the experimental structure. The anharmonic O--H stretching vibrations in the crystal are presented and found to be very close to results from calculations on molecular clusters. The electronic band and density-of-states spectra are discussed. Model calculations on a hydrogen fluoride chain were used to rationalize the results. IntroductionThe water molecule and its unique binding properties are of interest to both experimentalists and theoreticians. Crystalline hydrates have consequently been extensively characterized experimentally. The effect of the crystalline environment on the structure, vibrations, electron density, quadrupolar coupling constants etc. of the water molecule have been investigated in many hundreds of diffraction and spectroscopic studies (e.g. Falk & Knop, 1973; Acta Crvstallographica Section B ISSN 0108-7681 ©i994 LARS OJAMAE et al. 269 Olovsson & J6nsson, 1976; Berglund, Lindgren & Tegenfeldt, 1978a,b; Chiari & Ferraris, 1982;Hermansson, 1984;Mikenda, 1986;Lutz, 1988). Among the crystalline hydrates one finds examples of a wide variety of water environments, from very weakly to very strongly bound molecules. This is reflected in the broad ranges of measured H-..O hydrogen-bond distances (from, say, 3.2 down to 1.65 A0, OH vibrational frequency downshifts (from -150 to --1000 cm-~) and deuteron quadrupole coupling constants (from 240 down to -170 kHz for the most strongly bound water molecules).The theoretical approach to the study of hydrates has commonly been to use q...

Electric field gradient calculations forLixTiS2and comparison withLiBredow1, Heitjans2, Wilkening3 2004Phys. Rev. B916870View full textAdd to dashboardCite

“…28 Therefore we performed a basis set optimization for LiTiS 2 . The following basis sets (in the Pople notation 49 ) served as starting points for our investigation: 8-6411G31d for Ti, 50 and 8-6311G* for S. 51,52 Three basis sets from the literature were considered for Li, 6-11G, 12,53 7-11G, 54 and a fully uncontracted basis. 55 Three quantum-chemical methods were compared; (a) the Perdew-Wang Generalized Gradient Approximation (PWGGA) of DFT; 56 (b) a HF-DFT hybrid approach (HFPW), where the electron exchange term is a linear combination of the Perdew-Wang functional (0.8) and the exact HF term (0.2) and electron correlation is treated with the Perdew-Wang functional; and (c) the HF method, combined with the Perdew-Wang correlation functional ͑HF+ PW͒.…”

“…The 6-11G basis was optimized for Li+ in LiO(OH). 53 A larger contraction for the inner 1s shell was used in the DZVP2 or 7-11G basis (D) of Godbout et al 54 A fully uncontracted basis consisting of 18s shells 55 was modified by removing the two outermost shells and augmenting the remaining three most diffuse s shells with p shells (E).…”

Structure and electronic properties of MNO3 (M: Li, Na, K, NH4) under pressure: DFT-D study

“…The advantage of the LCAO-basis is the possibility of direct analysis of local characteristics of the electron density distribution (bond populations, atomic charges). In the calculations used basis sets [52][53][54][55][56] and generalized-gradient approximation functional of Perdew, Burke, and Ernzerhof (PBE-GGA) [49]. We also used B3LYP hybrid density functional [57] for calculations of band gaps.…”

Thermodynamic study of reconstructed crystal surfaces.

“…In turn, AO's (basis set) are linear combinations of Gaussiantype functions (GTF, the product of a Gaussian times a real solid spherical harmonic to give s-, p-, and d-type AO's). In the present case, Li is described with a 6-11G* basis [19]. It consists of six contracted GTF's for the description of the core shell, and two uncontracted sp and one d functions for the valence shell.…”