Hartree-Fock and DFT calculations of quadrupole coupling constants in water clusters and ice

Periodic ab initio calculations of the O-17 and H-2 quadrupole coupling constants (QCC) and their shifts have been performed for ice VIII and

ice IX. Cluster calculations were done for smaller water clusters and

chains. The ice Vm crystal structure was optimized at the Hartree-Fock

and BLYP (DFT) levels with a 6-311g** basis. Out of the methods

tested here the Hartree-Fock-computed QCC shifts based on the fully

optimized Hartree-Fock structure are those which overall agree best

(within 5-10%) with experimental shifts. The crystalline surroundings

outside the tetrahedral ice cluster accounts for between a third and a

half of the observed experimental QCC downshifts for both oxygen and

hydrogen in ice VIII. (C) 1999 Elsevier Science B.V. All rights

reserved.