Ab initio SCF calculations were performed in the unit cell environment, making use of the periodic behaviour to compute a wave-function for the bulk material. Electric field gradient (EFG) calcula tions were performed on the resulting wave-functions, and these are compared with experimental quadrupole coupling parameters. Examples of inorganic molecular and ionic crystals (nitrogen, chlorine and lithium nitride) and minerals or partially covalent lattice structures (alumina, petalite, a-quartz, boron oxide, boron nitride and sulphur nitride) are described. The effects of the basis set in these calculations are considered, and the limitations imposed by the nature of the calculation are described.

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We present ab initio Hartree-Fock lattice calculations performed in the unit cell environment, to compute a wave-function and the derived electric field gradients for the bulk material. These calculations differ from cluster calculations by including the effects of more distant neighbour molecules. Examples considered are ammonia, formamide, oxamide, urea, thiourea, uracil, para-banic acid, alloxan, guanidine bicarbonate and melamine.

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