A method for computing electron momentum densities and Compton profiles from ab initio calculations is presented. Reciprocal space is divided into optimally-shaped tetrahedra for interpolation, and the linear tetrahedron method is used to obtain the momentum density and its projections such as Compton profiles. Results are presented and evaluated against experimental data for Be, Cu, Ni, Fe3Pt, and YBa2Cu4O8, demonstrating the accuracy of our method in a wide variety of crystal structures.

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractFirst principles calculations are performed using density functional theory and density functional perturbation theory for SnAs. Total energy calculations show the first order phase transition from an NaCl structure to a CsCl one at around 37 GPa, which is also confirmed from enthalpy calculations and agrees well with experimental work. Calculations of the phonon structure and hence the electron-phonon coupling, λ ep , and superconducting transition temperature, T c , across the phase diagram are performed. These calculations give an ambient pressure T c , in the NaCl structure, of 3.08 K, in good agreement with experiment whilst at the transition pressure, in the CsCl structure, a drastically increased value of T c = 12.2 K is found. Calculations also show a dramatic increase in the electronic density of states at this pressure. The lowest energy acoustic phonon branch in each structure also demonstrates some softening effects. Electronic structure calculations of the Fermi surface in both phases are presented for the first time as well as further calculations of the generalised susceptibility with the inclusion of matrix elements. These calculations indicate that the softening is not derived from Fermi surface nesting and it is concluded to be due to a wavevector-dependent enhancement of the electron-phonon coupling.