Basis set convergence in extended systems: infinite hydrogen fluoride and hydrogen chloride chains

Basis set convergence of the Hartree–Fock and the correlation energy is examined for the hydrogen bonded infinite bent chains (HF)∞ and (HCl)∞. We employ series of correlation consistent basis sets up to quintuple ζ quality together with a coupled cluster method (CCSD) to describe electron correlation on ab initio level. The Hartree–Fock energy converges rapidly with increasing basis set quality whereas the correlation energy is found to be slowly convergent for the same series of basis sets. We study basis set extrapolation for (HF)∞ and (HCl)∞ and show that it substantially enhances the accuracy of both the Hartree–Fock and the correlation energy in extended systems.