A direct-operation time-dependent method for calculating absorption spectra involving multiple electronic states and its application to trans-OsO2(oxalate)22-

In this paper we present a new method for calculating electronic spectra of molecules adequately represented by simple model potentials. The absorption spectrum is obtained from the Fourier transform of a correlation function in the standard fashion. The correlation function is computed using a Chebyshev expansion and matrix-vector products are evaluated with the direct-operation method. The method is applied to study the spectrum of trarzs-OsO2 (oxalate)(2)(2-). We use two two-dimensional harmonic excited diabetic electronic states coupled by a constant term. In this case the direct-operation method is efficient because of the simplicity of the potentials. We explain the vibronic patterns observed at low temperature and the unusually low intensity of the first peak of the first charge-transfer band. (C) 1999 Elsevier Science B.V. All rights reserved.