Nonorthogonal ultralocalized functions and fitted Wannier functions for local electron correlation methods for solids

摘要

Despite the formal exponential decay behavior of Wannier functions (WFs),their spatial extent,which is a key parameter determining the computational cost of local correlation calculations for solids,is still rather large.The problems with the localization of the WFs can partly be attributed to their mutual orthogonality.Possibilities of reduction of the spatial extent of the WFs without losing the accuracy of the calculations are investigated.A method for generation of non-orthogonal ultralocalized functions based on maximization of their Lowdin populations is developed.A scheme for fitting of the WFs and nonorthogonal localized functions with a limited support is proposed.The calculations show that by combining both techniques one can obtain quite compact linearly independent localized functions,which may significantly decrease the computational cost in post-HF calculations.