The fcc-bcc structural transition .1. A band theoretical study for Li, K, Rb, Ca, Sr, and the transition metals Ti and V

Employing a high-precision band structure method (FP LAPW-full potential linearized augmented plane wave) we calculate the total energy variation along the tetragonal distortion path connecting the body centred cubic (bcc) and the face centred cubic (fee) structures, The total energy along this Bain transformation is calculated, varying c/a and volume, providing a first-principles energy surface which has two minima as a function of c/a. These are shallow and occur for the sp metals at the two cubic structures, while Ti (V) has a minimum at fee (bcc) but a saddle point (i.e. a minimum in volume and a maximum with respect to cia) at the other cubic structure. These features can be analysed in terms of an interplay between the Madelung contribution and the band energies. Our total energy results allow us to calculate the elastic constants C-11 and C-12 and to study the influence of pressure on the phase stability. These energy surfaces will be used in part II of this paper to investigate finite-temperature effects by mapping them to a Landau-Ginzburg expansion.