CALCULATION OF THE NONLINEAR SUSCEPTIBILITY FOR OPTICAL 2ND-HARMONIC GENERATION IN III-V SEMICONDUCTORS

We calculate both linear and nonlinear optical response in the static limit for AlP, AlAs, GaP, and GaAs in the local-density approximation with and without a scissors operator, including local-field effects. The calculation agrees with the measurement of Levine and Bethea to within 15%. The derivatives dln-chi-(2)/dlna, for lattice constant a, are predicted to be from 1.7 to 6.6 times the values obtainable from existing models. The calculated static dielectric constants epsilon-infinity are within 2% of measured values; calculated results for dln-epsilon-infinity/dlna are also presented. The scissors operator alters epsilon-infinity up to 25% but alters chi(2) by a factor of 2.