Efficient Calculations of Molecular Linear Response Properties for Spectral Regions

Molecular spectra can be determined from molecular response functions, by solving the so-called damped response equations using the complex polarization propagator approach. The overall structure of response equations is identical for variational wave functions such as the Hartree-Fock, multiconfiguration self-consistent field, and Kohn-Sham density functional theory, and the key program module is the linear response equation solver. We present an implementation of the solver using the algorithm with symmetrized vectors, optimized for addressing spectral regions of a width of some 5-10 eV and a resolution below 0.1 eV. The work is illustrated by the consideration of UV-vis as well as near carbon K -edge absorption spectra of the C60 fullerene. We demonstrate that it is possible to converge tightly response equations for hundreds of optical frequencies in resonance regions of the spectrum at a cost not much exceeding the solution of a single response equation in the nonresonant region. Our work is implemented in the molecular orbital based module of the Dalton program and serves as a documentation of the code distributed in the Dalton2013 release version.