P. Ordejon et al., UNCONSTRAINED MINIMIZATION APPROACH FOR ELECTRONIC COMPUTATIONS THAT SCALES LINEARLY WITH SYSTEM SIZE, Physical review. B, Condensed matter, 48(19), 1993, pp. 14646-14649
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.