The electronic structures of lizardite (Mg3Si2O5(OH)(4)), characterized by the periodic Hartree-Fock method using a large basis set, are compared for two structure refinements performed at 0 and 1.25 GPa. The total energies of one hydrogen bond (HB) evaluated for the two structures are 29 and 43 kJ/mol(-1), respectively. The strengthening of the HB qualitatively agrees with the negative shift of the stretching frequency in infrared spectra. The strengthening is characterized by means of difference electron density maps (both SCF-atomic and 3D-2D), showing that the region of the HE is depleted of the electron density, and the degree of depletion indicates the strength of the HE. The maximum value of the 3D-2D depletion at 1.25 GPa is 0.020 e/bohr(3) compared to 0.015 e/bohr(3) obtained for the weaker HE at zero pressure. Pressure-induced changes are documented with charge density maps, net atomic charges, overlap populations, and partial density of states. The positions of the s bands are shown to be driven by the covalency/ionicity of the bonding with increased ionicity causing the destabilization of energy levels.
