Issue 21, 2012

Hybrid one-electron/many-electron methods for ionized states of molecular clusters

Abstract

To describe singly-ionized states of molecular clusters we devised an effective Hamiltonian approach that combines (1) accurate monomer ionization potentials from many-electron wave functions with (2) polarization shifts and (3) effective monomer couplings obtained from a simple one-electron approach (the superposition-of-fragment-states (SFS) method [Valeev et al., J. Am. Chem. Soc., 2006, 128, 9882]). The accuracy of the intermolecular coupling parameters evaluated with SFS Hartree–Fock (HF) and Density-Functional-Theory (DFT) variants was evaluated for several weakly-bound dimers and compared against the state-of-the-art equation-of-motion ionization-potential coupled-cluster singles and doubles (EOM-IP-CCSD) data of Krylov and co-workers. The SFS–HF method produces coupling integrals accurate to a few percent, whereas SFS–DFT predictions are substantially worse. A hybrid approach combining SFS–HF couplings and shifts with EOM-IP-CCSD ionization potentials of monomers (denoted as SFS-EOM-IP-CCSD) was applied to ionized states of two conformers of a benzene dimer and ten representative DNA base pairs. The 16 considered SFS-EOM-IP-CCSD ionization potentials of the benzene dimer differed from the reference EOM-IP-CCSD IPs of Krylov and co-workers [Pieniazek et al., J. Chem. Phys. 2007, 127, 044317; Bravaya et al., Phys. Chem. Chem. Phys. 2010, 12, 2261] by less than 0.1 eV on average, and at most by 0.2 eV. For the DNA base pairs the mean absolute (median) deviation of the SFS-EOM-IP-CCSD IPs was 0.27 (0.23) eV; several deviations for non-Koopmans states were as large as 0.9 eV. The SFS-EOM-IP-CCSD method can be readily applied to large molecular clusters with computational effort scaling cubically with the size of the cluster.

Graphical abstract: Hybrid one-electron/many-electron methods for ionized states of molecular clusters

Article information

Article type
Paper
Submitted
23 Jan 2012
Accepted
17 Apr 2012
First published
18 Apr 2012

Phys. Chem. Chem. Phys., 2012,14, 7863-7871

Hybrid one-electron/many-electron methods for ionized states of molecular clusters

J. Zhang and E. F. Valeev, Phys. Chem. Chem. Phys., 2012, 14, 7863 DOI: 10.1039/C2CP40222J

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