UNCONSTRAINED MINIMIZATION APPROACH FOR ELECTRONIC COMPUTATIONS THAT SCALES LINEARLY WITH SYSTEM SIZE

We present a method for the calculation of total energies and forces t hat scales linearly with the number of atoms in the system. The key po ints are (i) an unconstrained conjugate gradient minimization of the e lectronic energy that avoids the need of explicit orthonormalization, and (ii) description of the electrons in terms of localized wave funct ions, truncated beyond a radius R(c). The method is variational, givin g an upper bound to the exact total energy, and is exact as R(c) --> i nfinity. We test the method for a model tight-binding Hamiltonian, and in full ab initio molecular-dynamics calculations.