NONLOCAL PSEUDOPOTENTIALS IN COMPLEX BAND-STRUCTURE AND PHOTOEMISSIONCALCULATIONS

Based on a recently proposed localization procedure, a nonlocal pseudo potential scheme is derived to calculate potential coefficients V(<(GG )over right arrow>)((k) over right arrow) which can be decomposed into terms, each being quadratic in (k) over right arrow and multiplied by a function of ((G) over right arrow-<(G)over right arrow '>), thus ma king them applicable to some important cases where local potential coe fficients are required. Electronic structure calculations for semicond uctors are in agreement with well-known semiempirical local pseudopote ntial band structures, as shown for GaAs. Nevertheless, the potential may significantly deviate from the semiempirical results. In order to; test wave functions and transition probabilities, we prove the succes s of the procedure in a more troublesome case, i.e., applying it to a transition metal compound as the experimentally well-investigated laye red crystal TiSe2, which up to now was not treated with a pseudopotent ial. Photoemission spectra within the one-step model are presented usi ng Pendry's method of complex band-structure calculation. The latter f ormalism had to be slightly generalized for the quasilocal properties of the potential. The agreement of the spectra with experimental data shows this method to be a reliable and practical tool to use nonlocal pseudopotentials for conduction-band wave functions of electron spectr oscopies.