EXTRACTING ACCURATE BOUND-STATE SPECTRA FROM APPROXIMATE WAVE-PACKET PROPAGATION USING THE FILTER-DIAGONALIZATION METHOD

We present an extension of the filter-diagonalization (FD) approach wh ich allows the extraction of accurate bound-state spectra from a time- dependent wave function determined by an approximate propagation schem e. To investigate the method, an approximate wave function is generate d by a wave packet propagation on a two-dimensional potential energy s urface for the LiCN molecule, employing a second-order differencing in tegrator with large step size. When applied to this inaccurate wave fu nction, our formulation of the FD technique is capable of yielding eig enenergies considerably more precise than those obtained with the orig inal FD method, while the effort is almost the same. The present FD sc heme contains some additional refinements that increase the method's e fficiency, accuracy, and practicability. We demonstrate that the accur acy of the FD procedure can be improved by using cosinetype filters. T he quality of different variational principles employed to determine t he eigenenergies is examined. These variational principles can also be utilized to estimate the error of the energies and intensities inexpe nsively and reliably. (C) 1998 American Institute of Physics. [S0021-9 606(98)01334-8].