A new implementation of the second-order polarization propagator approximation (SOPPA): The excitation spectra of benzene and naphthalene

Abstract

We present a new implementation of the second-order polarization propagator approximation (SOPPA) using a direct linear transformation approach, in which the SOPPA equations are solved iteratively. This approach has two important advantages over its predecessors. First, the direct linear transformation allows for more efficient calculations for large two particle–two hole excitation manifolds. Second, the operation count for SOPPA is lowered by one order, to N5. As an application of the new implementation, we calculate the excitation energies and oscillator strengths of the lowest singlet and triplet transitions for benzene and naphthalene. The results compare well with experiment and CASPT2 values, calculated with identical basis sets and molecular geometries. This indicates that SOPPA can provide reliable values for excitation energies and response properties for relatively large molecular systems.

Large-scale calculations of excitation energies in coupled cluster theory: The singlet excited states of benzene

“…The RPA results of Packer et al are of the same quality as the CCS results ͑the 2 1 E 1u state is again an exception͒. 57 Note that no results are given for the 2 1 E 2g state since it is not included in the investigation of Packer et al, probably because of the large contributions from double excitations. The SOPPA excitation energies are lower than the CC energies for all excitations.…”

“…56 and the RPA and SOPPA calculations of Ref. 57 have been carried out using the same ANO1 basis set and the same geometry as in our calculations and a direct comparison with these results is thus possible. For all excitations except the 2 1 E 2g valence state, we expect as discussed in the previous section that the CC3 excitation energies are very close to the exact results in the same basis and at the same molecular geometry.…”

“…We thank Berta Fernandez for critical reading of the manuscript, and Erik K. Dalskov for a preprint of Ref. 57.…”

“…Benzene is one of the most investigated molecules both theoretically [52][53][54][55][56][57][58][59][60] and experimentally. [60][61][62][63][64][65][66][67][68][69][70][71][72][73][79][80][81][82] However, there are still many unsolved problems in the benzene spectrum.…”

A theoretical study of the 1B2u and 1B1u vibronic bands in benzene

“…8 Assignment of the bands in the electronic spectrum of benzene has been much discussed since the early experimental works. 3 Recent ab initio calculations [9][10][11][12][13] led to unambiguous assignments of the main vertical features ͑also Rydberg states͒, except perhaps for the 1 E 2g state, a multiconfigurational state which only the CASSCF/CASPT2 method 9,10 seems to treat properly.…”