Evolution of the (hyper)polarizability with the size and periodicity of the system. A model investigation from the LiF molecule to the LiF 3D crystal

Abstract

A finite field (FF) perturbation method, implemented in the CRYSTAL program, is used to investigate the evolution of the response to an applied electric field of systems of increasing size and dimensionality. LiF molecules, chains, slabs and bulk have been considered as model systems. (LiF)$_M$ molecules of increasing length are compared with the periodic infinite linear chain data; systems containing an increasing number of parallel linear chains are compared with the single layer slab, and slabs of increasing thickness are compared with bulk results. The same hamiltonian (Hartree-Fock), Li-F distance and basis set have been used for all systems. Sharp variations are observed in the response properties along the series (from the molecule to the 3D crystal), that are not the same for the parallel and perpendicular components of the tensors. In particular the (hyper)polarizability tensor components can vary by as much as a factor 8.