FIRST-ORDER CORRECTIONS TO RANDOM-PHASE-APPROXIMATION GW CALCULATIONSIN SILICON AND DIAMOND

We report on ab initio calculations of the first-order corrections in the screened interaction W to the random-phase approximation polarizab ility and to the GW self-energy, using a noninteracting Green's functi on, for silicon and diamond. It is found that the first-order vertex a nd self-consistency corrections to the polarizability largely compensa te each other. This does not hold, however, for the first-order correc tions to the GW gap. For silicon the compensation between the first-or der vertex and self-consistency correction contributions to the gap is only about 35%, while for diamond it is even absent. The resulting ga p values are significantly and systematically too large, the direct ga ps for silicon and diamond being 0.4 eV and 0.7 eV larger than their G W values, respectively. The success of GW in predicting electronic pro perties of, e.g., silicon and diamond can therefore apparently not be understood in terms of ''small'' corrections to GW to first order in W using a noninteracting Green's function. [S0163-1829(98)01819-0].