QUADRUPOLE COUPLING IN SOME H-BONDED ORGANIC-SYSTEMS BY AB-INITIO LATTICE CALCULATIONS OF ELECTRIC-FIELD GRADIENTS

We present ab initio Hartree-Fock lattice calculations performed in th e unit cell environment, to compute a wave-function and the derived el ectric field gradients for the bulk material These calculations differ from cluster calculations by including the effects of more distant ne ighbour molecules. Examples considered are ammonia, formamide, oxamide , urea, thiourea, uracil, parabanic acid, alloxan, guanidine bicarbona te and melamine.