Improving the efficiency of FP-LAPW calculations

The full-potential linearized augmented-plane wave (EP-LAPW) method is well known to enable most accurate calculations of the electronic structure and magnetic properties of crystals and surfaces. The implementation of atomic forces has greatly increased its applicability, but it is still generally believed that FP-LAPW calculations require substantial higher computational effort compared to the pseudopotential plane wave (PPW) based methods. In the present paper we analyze the FP-LAPW method from a computational point of view. Starting from an existing implementation (WIEN95 code), we identif ied the time consuming parts and show how some of them can be formulated mo re efficiently. In this context also the hardware architecture plays a crucial role. The re maining computational effort is mainly determined by the setup and diagonal ization of the Hamiltonian matrix. For the latter. two different iterative schemes are compared. The speed-up gained by these optimizations is compare d to the runtime of the "original" Version of the code, and the PPW approac h. We expect that the strategies described here, can also be used to speed up other computer codes, where similar tasks must be performed. (C) 2000 El sevier Science B.V. All rights reserved.