AB-INITIO CALCULATION OF VIBRATIONAL CIRCULAR-DICHROISM SPECTRA USING GAUGE-INVARIANT ATOMIC ORBITALS

Atomic axial tensors (AATs) calculated using gauge-invariant atomic orbitals (GIAOs) are more accurate than AATs calculated using field-independent atomic orbitals (FIAOs). Consequently, vibrational rotational strengths and vibrational circular dichroism (VCD) intensities are more accurately predicted using GIAO-based AATs. The increase in accuracy resulting from the use of GIAOs depends on the basis set size. We report calculations of the vibrational rotational strengths and VCD spectra of three chiral moIecules-trans-2,3-d(2)-oxirane, 4-methyl-2-oxetanone, and 6,8-dioxabicydo[3.2.1]octane-at the 6-31G'' basis set level. Harmonic force fields and atomic polar tensors are calculated via density functional theory using the B3LYP functional. Distributed AATs are calculated at the SCF level using both GIAOs and FIAOs. Comparison to experimental VCD spectra (and, in the case of trans-2,3-d(2)-oxirane, to calculations at the TZ2P basis set level) demonstrates the significantly greater accuracy of the calculations using GIAOs.