Ab initiostudy of the structural properties of LiF, NaF, KF, LiCl, NaCl, and KCl

The lattice energy (LE), equilibrium lattice parameter (${\mathit{a}}_0$), elastic constants (${\mathit{C}}_{\mathit{i}\mathit{j}}$), and central-zone phonon frequencies (ν) of LiF, LiCl, NaF, NaCl, KF, and KCI have been evaluated with c r y s t a l, a periodic ab initio Hartree-Fock linear combination of atomic orbitals program. The mean error with respect to experiment is 5.7%, 3.4%, 14.6%, and 8.8% for LE, ${\mathit{a}}_0$, B [bulk modulus; B=1/3(${\mathit{C}}_{11}$+2${\mathit{C}}_{12}$)], and ν, respectively. The errors increase systematically with increasing size of the cation or anion. Correlation effects (both intraionic and interionic) are the main reason for the discrepancies with respect to experiment.