The point charge model of nuclear quadrupoles: How and why does it work

The point charge model of nuclear quadrupoles is analyzed beyond the multip ole approximation. The effect of the short-range expansion terms is shown t o be responsible for the contamination of the calculated electric field gra dients. Several regularities observed in earlier numerical calculations are elucidated and their analysis helps to devise proper computational strateg ies. The use of the point charge nuclear quadrupole model is strongly advoc ated in approximate relativistic calculations of electric field gradients a t heavy nuclei. (C) 2000 American Institute of Physics. [S0021-9606(00)0040 2-5].