EFFICIENT AB-INITIO METHOD FOR THE CALCULATION OF FREQUENCY-DEPENDENT2ND-ORDER OPTICAL-RESPONSE IN SEMICONDUCTORS

The development of a method for calculating the frequency-dependent se cond harmonic generation coefficient of insulators and semiconductors based on the self-consistent linearized muffin-tin orbitals band struc ture method is reported. The calculations are at the independent parti cle level and are based on the formulation introduced by Aversa and Si pe [Phys. Rev. B 52, 14 636 (1995)]. The terms are rearranged in such a way as to exhibit explicitly all required symmetries including the K leinman symmetry in the static limit. Computational details and conver gence tests are presented. The calculated frequency-dependent chi((2)) (-2 omega,omega,omega) for the zinc-blende materials GaAs, Gap and wur tzite GaN and ALN are found to be in excellent agreement with that obt ained by other first-principles calculations when corrections to the l ocal density approximation are implemented in the same manner, namely, using the ''scissors'' approach. Similar agreement is found for the s tatic values of chi((2)) for zinc-blende GaN, AlN, BN, and SiC. The st rict validity of the usual ''scissors'' operator implementation is, ho wever, questioned. We show that better agreement with experiment is ob tained when the corrections to the low-lying conduction bands are appl ied at the level of the Hamiltonian, which guarantees that eigenvector s are consistent with the eigenvalues. Results are presented for the f requency-dependent chi((2))(-2 omega,omega,omega) for 3 C-SiC. The app roach is found to be very efficient and flexible, which indicates that it will be useful for a wide variety of material systems including th ose with many atoms in the unit cell. [S0163-1829(98)04107-1].