DIRECT MINIMIZATION OF THE ENERGY IN DENSITY-FUNCTIONAL THEORY

The minimization of the energy functional of the first-order density m atrix gamma(r,r') is achieved using unitary transformations applied to gamma. Equivalently, such transformations can be carried out also on one-electron orbitals (natural orbitals) and their occupation (integer or non-integer) numbers. The conventional local density approximation based on the electron density rho(r) is then considered as a special case. The direct minimization of the energy functional of rho with res pect to the parameters of the unitary transformation leads to stationa ry conditions that are all equivalent to the Kohn-Sham equations. Prel iminary numerical tests show that the proposed algorithms for the dire ct minimization of the energy work in a satisfactory manner. (C) 1994 John Wiley & Sons, Inc.