1ST-PRINCIPLES PSEUDOPOTENTIAL CALCULATIONS FOR HYDROGEN IN 4D-TRANSITION METALS .1. MIXED-BASIS METHOD FOR TOTAL ENERGIES AND FORCES

A first-principles study of hydrogen in transition metals within the framework of the Born-Oppenheimer and local density-functional approximations using a mixed-basis pseudopotential method is presented in this work, which consists of two parts. In this first part our computational techniques are outlined. The features of the norm-conserving ionic pseudopotentials, the mixed basis and the calculation of total energies are summarized. A mixed-basis formalism for the calculation of forces on atoms in crystals, using the Hellmann-Feynman theorem and including contributions originating from the atom-centred localized functions in the mixed basis, is described in detail and applied to the example of restoring forces in PdH. An application to a study of vibrational properties of hydrogen isotopes in Pd and Nb will follow in the second part.