Coupled perturbed Hartree-Fock for periodic systems: the role of symmetry and related computational aspects.

A general and efficient implementation of the coupled perturbed Hartree-Fock (CPHF) scheme in the CRYSTAL06 code that applies to systems periodic in one dimension (polymers), two dimensions (slabs), three dimensions (crystals) and, as a limiting case, zero dimension (molecules) is presented. The dielectric tensor of large unit cell systems such as boehmite (gamma-AlOOH, 8 atoms/cell), calcite (CaCO3, 10 atoms/cell), and pyrope (Mg3Al2Si3O12, 80 atoms/cell) has been computed. Results are well converged with respect to the computational parameters, in particular, to the number of k points in the reciprocal space and tolerances used in the truncation of the Coulomb and exchange series, showing that the same standard computational conditions used for the self-consistent-field (SCF) step can also be used safely in a CPHF calculation. Point symmetry, being so important in determining crystal properties, also reduces dramatically the computational cost both of the preliminary SCF step and the CPHF calculation, so that the dielectric tensor for large unit cell systems such as pyrope can be computed within 2 CPU hours on a single processor PC.