Quantum-mechanical simulations have been performed to investigate pressure effects on the crystal geometry, chemical bonding, and the electronic structure of anatase ${\mathrm{TiO}}_2.$ Total energy calculations are carried out using the density functional formalism under the nonlocal B3LYP approximation. The optimized unit cell equilibrium parameters and the bulk and linear compressibilities are determined to be in good agreement with recent experimental data. The topology of the electron density is examined by means of the atoms in molecules (AIM) theory. Computed AIM charges and topological properties of the bond critical points reveal a partially ionic behavior of the crystal that complements the description obtained from the band structure and the projected density of states analysis. A microscopic interpretation of the crystal response to hydrostatic pressure is given in terms of the elementary polyhedra and the AIM atomic volumes that fill the unit cell space.

• Received 30 May 2001

DOI:https://doi.org/10.1103/PhysRevB.64.184113