Real-space method for calculation of the electric field gradient: comparison with k-space results

Results for the electric field gradient (EFG) in eight HCP metals are obtained using the linear muffin-tin orbital (LMTO) atomic sphere approximation (ASA) method and a recently proposed LMTO ASA recursion scheme. In all cases the k-space LMTO ASA results for the EFG agree well with those obtained using the real-space procedure and a first-order LMTO ASA tight-binding Hamiltonian with interactions limited to first neighbours. This is remarkable considering that the EFG is determined by differences between partial occupation numbers, which are of order of a hundredth of an electron and shows that the first-order Hamiltonian is very reliable. A comparison with more precise full-potential linear augmented plane-wave calculations and experimental values shows reasonably good agreement. This opens the way for predictions of the EFG in more complicated and disordered systems.