Modeling Charge Resonance in Cationic Molecular Clusters: Combining DFT-Tight Binding with Configuration Interaction

Abstract

In order to investigate charge resonance situations in molecular complexes, Wu et al. (J. Chem. Phys. 2007, 127, 164119) recently proposed a configuration interaction method with a valence bond-like multiconfigurational basis obtained from constrained DFT calculations. We adapt this method to the Self-Consistent Charge Density-Functional-based Tight Binding (SCC-DFTB) approach and provide expressions for the gradients of the energy with respect to the nuclear coordinates. It is shown that the method corrects the wrong SCC-DFTB behavior of the potential energy surface in the dissociation regions. This scheme is applied to determine the structural and stability properties of positively charged molecular dimers with full structural optimization, namely, the benzene dimer cation and the water dimer cation. The method yields binding energies in good agreement with experimental data and high-level reference calculations.

Proton transfer or hemibonding? The structure and stability of radical cation clusters

“…While there has been a large number of studies devoted to study these systems, they have predominantly focused on dimers. [2][3][4][5][6][7][8][9][10][11][13][14][15][16][17][18][20][21][22][25][26][27] The most extensively studied radical cation cluster is (H 2 O) 2 . + , and a wide variety of methods have been applied to characterise its structure.…”

“…+ , and a wide variety of methods have been applied to characterise its structure. 2,5,7,8,10,[13][14][15]17,18,21,25,26 The study of (H 2 O) 2 . + has proved to be a challenge for density functional theory (DFT), and many commonly used exchange-correlation functionals wrongly predict the hemibonded structure to be more stable than the proton transfer one.…”

Electronic spectra of cationic PAH and PAH clusters

“…If M + is in one excited state, M + * , one electron from a lower π orbital -lying below the HOMO -has been promoted to a higher-lying orbital. Thus, on the one hand, in the ground electronic state of the dimer cation, the two molecules play equivalent roles and a charge resonance (CR) effect takes place (Rapacioli et al 2011). On the other hand, when an electronic transition is induced in the cationic dimer (of the type HOMO-n to HOMO in the present case), the two molecules are not equivalent and a locally-excited state is involved, in which the promoted orbital originates from the molecule which carries the charge (if not it would involve a promotion to a π * orbital, lying at a much higher energy).…”

Perspectives from Quantum Chemistry for molecules and nanograins with astrophysical Interest

“…Such configurations do not present charge delocalization and can be obtained from constrained DFT calculations. This is the basis of the CDFT-CI method [140][141][142][143][144] which has been recently adapted for the DFTB framework (DFTB-VBCI see [145]). As can be seen from Figure 16, a correct behavior of the dissociation energy curve is recovered and the binding energy (corresponding to a so-called parallel displaced isomer) is in agreement with the experimental results.…”

“…BOP were first 06003-p.17 Figure 16. Dissociation potential energy curves of the cationic benzene dimer in the stacked sandwich configuration calculated with SCC-DFTB and DFTB-VBCI [145] approaches, compared with experimental binding energies/enthalpy taken from (a) (Ref [146]), (b) (Ref [147]) and (c) (Ref [148]). defined by Abell [151] under the form…”