Abstract

A multiresolution density-matrix wavelet approach to electronic-structure calculations is proposed. A separable multidimensional biorthogonal interpolating multiwavelet and scaling representation of the Hamiltonian operator is introduced in which individual operator elements can be calculated locally at any scale. Issues regarding this representation are discussed, such as its low complexity in higher dimensions and its direct relation to finite-difference schemes. The density matrix is calculated via polynomial expansions in terms of the Hamiltonian. The expansions are improvements of the McWeeny purification within a grand canonical ensemble and are shown to be up to 20% more efficient in the number of matrix-matrix multiplications. The efficiency of the multiresolution representation of the density matrix compared to a real-space representation is analyzed. Within the multiresolution wavelet representation it is shown how the sparsity of the density matrix is preserved for localized insulating systems as well as for itinerant metallic systems. This is not possible within a real-space representation of the density matrix which has a very slow decay of its elements in the metallic phase. This makes the multiresolution approach very attractable for linear- or close to linear-scaling electronic-structure calculations.

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