Unrestricted algebraic diagrammatic construction scheme of second order for the calculation of excited states of medium-sized and large molecules

摘要

An unrestricted version of the algebraic diagrammatic construction u0001ADCu0002 scheme of thenpolarization propagator in second order perturbation theory u0003UADCu00012u0002u0004 is derived via thenintermediate state representation. The accuracy of the extended UADCu00012u0002-x approach is evaluatednby comparison of computed excitation energies of 11 medium-sized radicals with theirncorresponding experimental literature values and with excitation energies computed atnequation-of-motion-CCSD u0001coupled clusters singles and doublesu0002 level of theory. Overall, ournnumerical tests show that UADCu00012u0002-x exhibits an averaged mean deviation in the excitation energiesnof only 0.3–0.4 eV compared to experimental gas phase data. It provides thus an alternative toncoupled-cluster based approaches for the calculation of excited states of medium-sized open-shellnmolecules.