AB-INITIO CALCULATION OF ELECTRONIC CIRCULAR-DICHROISM FOR TRANS-CYCLOOCTENE USING LONDON ATOMIC ORBITALS

The second-quantization magnetic dipole operator that arises when Lond on atomic orbitals are used as basis functions is derived. In atomic u nits, the magnetic dipole operator is defined as the negative of the f irst derivative of the electronic Hamiltonian containing the interacti on with the external magnetic field. It is shown that for finite basis sets, the gauge origin dependence of the resulting magnetic dipole op erator is analogous to that of the exact operator, and that the derive d operator converges to the exact operator in the limit of a complete basis set. It is also demonstrated that the length expression for the rotatory strength in linear response calculations gives gauge-origin-i ndependent results. Sample calculations on ti ans-cyclooctene and its fragments are presented. Compared to conventional orbitals, the basis set convergence of the rotatory strengths calculated in the length for m using London atomic orbitals is favourable. The rotatory strength ca lculated for trans-cyclooctene agrees nicely with the corresponding ex perimental circular dichroism spectrum, but the spectra for the fragme nt molecules show little resemblance with that of trans-cyclooctene.