Modelling excited states of weakly bound complexes with density functional theoryTools Briggs, Edward A. and Besley, Nicholas A. (2014) Modelling excited states of weakly bound complexes with density functional theory. Physical Chemistry Chemical Physics, 16 (28). pp. 1445514462. ISSN 14639076
AbstractThe binding within the etheneargon and formaldehydemethane complexes in the ground and electronically excited states is studied with equation of motion coupled cluster theory (EOMCCSD), secondorder MøllerPlesset perturbation theory (MP2) and density functional theory with dispersion corrections (DFTD). Electronically excited states are studied within MP2 and KohnSham DFT formalisms by exploiting a procedure called the maximum overlap method that allows convergence of the relevant selfconsistent field equations to higher energy (or excited state) solutions. Potential energy curves computed using MP2 are in good agreement with the EOM CCSD calculations for both the valence and Rydberg excited states studied. For the DFTD approach, B3LYPD3/augccpVTZ calculations are found to be in agreement with EOMCCSD for the ground and valence excited states. However, for the π3s Rydberg state of etheneargon and the n3s Rydberg state of formaldehydemethane significant deviation is observed, and this disagreement with EOMCCSD is present for a variety of DFTD based approaches. Variation of the parameters within the D2 dispersion correction results in closer agreement with EOMCCSD for the Rydberg states but demonstrates that a different parameterisation from the ground state is required for these states. This indicates that timedependent density functional theory calculations based upon a DFTD reference may be satisfactory for excitations to valence states, but will potentially be inaccurate for excitations to Rydberg states, or more generally states were the nature of the electron density is significantly different from the ground state.
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