Band-structure perturbations in strained crystals. II. Shifts at the Fermi surface of Cu

In a previous paper, we described the use of a perturbation technique in conjunction with the modified-planewave method to calculate first-order changes in electronic energy levels for fcc crystals under hydrostatic, tetragonal, and trigonal strains. In the present paper this approach is applied to changes at the Fermi level of Cu. We outline the use of these shifts to estimate changes in extremal Fermi-surface areas which may then be compared with de Haas-van Alphen data. Results for the hydrostatic case compare reasonably well with other calculations and with observation. For the uniaxial-stress cases comparison is made with the calculation of Davis and with observation by taking the appropriate linear combination of our hydrostatic and tetragonal (trigonal) results. Reasonable agreement with the limited experimental values is obtained; agreement with Davis is reasonably good in two cases but poor in others.