2020/07/07 by Sarai Dery Folkestad, Henrik Koch, Folkestad, Sarai D. +1
Physics and Astronomy · Biochemistry, Genetics and Molecular Biology · Chemistry · #Spectroscopy and Quantum Chemical Studies #Electron Spin Resonance Studies #Photochemistry and Electron Transfer Studies
paper · pdf · doi:10.48550/arxiv.2007.03454
We present an implementation of equation-of-motion oscillator strengths for\nthe multilevel CCSD (MLCCSD) model where CCS is used as the lower level method\n(CCS/CCSD). In this model, the double excitations of the cluster operator are\nrestricted to an active orbital space, whereas the single excitations are\nunrestricted. Calculated nitrogen K-edge spectra of adenosine, adenosine\ntriphosphate (ATP), and an ATP-water system are used to demonstrate the\nperformance of the model. Projected atomic orbitals (PAOs) are used to\npartition the virtual space into active and inactive orbital sets. Cholesky\ndecomposition of the Hartree-Fock density is used to partition the occupied\norbitals. This Cholesky-PAO partitioning is cheap, scaling as\n\O(N3), and is suitable for the calculation of core excitations\nwhich are localized in character. By restricting the single excitations of the\ncluster operator to the active space, as well as the double excitations, the\nCCSD-in-HF model is obtained. A comparison of the two models---MLCCSD and\nCCSD-in-HF---is presented for the core excitation spectra of the adenosine and\nATP systems.\n