We consider the energy bands of quasielectrons and quasiholes in lithium hydride within the Coulomb-hole–plus–screened-exchange formalism. The crystal density matrix is expressed by means of localized Gaussian functions and off-diagonal terms are preserved and rigorously accounted for. Using a basis set of plane waves orthogonalized to the cation core wave function, we express the matrix elements of the nonlocal self-energy operator in analytic form, thus achieving high numerical accuracy with moderate computational labor. Our theoretical results for the quasiparticle band structure, the valence bandwidth, the energy gap, and exciton resonances are in good agreement with the available optical and photoemission data. Ab initio inclusion of the many-body effects is found to be a key point for a theoretical interpretation of experimental electron properties and transitions in LiH.
