AB-INITIO CALCULATION OF VIBRATIONAL ABSORPTION AND CIRCULAR-DICHROISM SPECTRA USING DENSITY-FUNCTIONAL FORCE-FIELDS - A COMPARISON OF LOCAL, NONLOCAL, AND HYBRID DENSITY FUNCTIONALS

We report predictions of the unpolarized vibrational absorption and vi brational circular dichroism spectra of 10 chiral molecules based on h armonic force fields calculated ab initio using density functional the ory. The molecules are 1, oxirane (ethylene oxide)-trans-2,3-d(2); 2, methyloxirane (propylene oxide); 3, trans-2,3-dimethyloxirane; 4, tran s-2,3-dimethyloxirane-2-d(1);5, trans-2,3-dimethyloxirane-trans-2,3-d( 2); 6, methylthiirane (propylene sulfide); 7, trans-2, 3-dimethylthiir ane; 8, trans-2,3-dimethylthiirane-trans-2,3-d(2); 9, cyclopropanet-tr ans-1,2-d(2); 10, cyclopropane-anti-1,2,3-d(3)-1-C-13. Large TZ2P basi s sets are used to minimize basis set error. Three density functionals are employed: (1) the local spin density (LSDA) functional, (2) the B ecke-Lee-Yang-Parr (BLYP) nonlocal functional, and (3) the Becke 3-Lee -Yang-Parr (B3LYP) hybrid functional. Predicted spectra are sensitive to the choice of density functional. Spectra predicted using the B3LYP functional are in the best agreement with experimental spectra while spectra predicted using the LSDA functional are in the worst agreement . Spectra predicted using the BLYP functional are more similar to thos e obtained using the B3LYP functional. We conclude that the relative a ccuracies of the functionals are B3LYP > BLYP much greater than LSDA.