Currently, the ab initio total energy consists of the density functional theory (DFT) total energy and additional contributions from van der Waals dispersion and zero­point vibrational energy. We have introduced a new contribution to the total energy, from electron­phonon interaction. Due to its greater sensitivity to crystal structure (than vdW and ZPVE), by including EPI, we have resolved decades­old controversies on the stable structure of important materials e.g., hexagonal silicon carbide, SiC­4H, (not cubic SiC­3C) and cubic boron nitride, cBN, (not hexagonal hBN) are stable. We have derived the EPI contributions to the electronic and phonon free energies, relying on P.B. Allen’s general formalism for interacting quasiparticles, to go beyond the standard Quasi­Harmonic Approximation, which is valid only for non­interacting quasiparticles. Our and Allen’s contributions, taken together, lay the foundation to go beyond QHA and include EPI contributions on all thermodynamic properties e.g., structural properties, and to determine, more accurately, the phase transition temperatures, pressures and phase boundaries, for all materials. We have proposed the equilibrium combination of doped Lanthanum gallate electrolyte and lanthanum­doped Ceria buffer layer for intermediate temperature solid oxide fuel cells so that, with time, additional phases that can reduce the fuel cell efficiency are not formed.