The charge transfer term

The charge transfer contribution CT may play an important role in some chemical processes. Intuitively, this term corresponds to the shift of some electronic charge from the occupied orbitals of a monomer to the empty orbitals of the other. In the variational decomposition schemes this effect can be separately computed by repeating the calculations on the dimer with deletion of some blocks in the Hamiltonian matrix of the system and tak- 

Jacopo Tomasi, Benedetta Mennucci, Chiara Cappelli 

We consider unnecessary to summarize the technical details they can be found in the source paper as well as in ref. [3] for the version we are resuming here. 

In standard perturbation theory (PT) methods, the CT term is not considered fliere are now PT methods able to evaluate it but they are rarely used in the modeling of interaction potentials for liquids. 

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The charge transfer term arises from the transfer of charge (i.e. electrons) from occupied molecular orbitals on one molecule to unoccupied orbitals on the other molecule. This contribution is calculated as the difference between the energy of the supermolecule XY when this charge transfer is specifically allowed to occur, and an analogous calculation in which it is not. 

Since the involved configuration function corresponds to the ligand-to-metal charge transfer (LMCT), its contribution is called the charge transfer term. 

Finally, the charge transfer term is evaluated using the semiem-pirical formalism implemented in the SIBFA force field (Gresh et al., 1979 Piquemal etal., 2007) ... 

After our implementation of GEM-0, we extended the Coulomb and exchange-repulsion terms to enable the use or arbitrary angular momentum Hermites (Cisneros et al., 2006b). However, both implementations only enabled energy calculations. In order to carry out MD simulations it is necessary to evaluate the associated forces efficiently. Until recently, it was impractical to do this since the anal3d ical form of the force for the charge-transfer term was unavailable. 

Waals parameters here contain what in quantum mechanics is the charge transfer term, and dispersion is always included in the van der Waals attraction anyway. In MM4, polarization is specifically included as a separate term throughout, so nothing special is needed for hydrogen bonding. ... 

The latter term represents the sum of the following individual energy components the electrostatic interaction E the polarization effect Fp i, due to polarization of the electronic distribution of A by the system of the electric charges of B, and vice versa the exchange repulsion term E and the charge transfer term K, ... 

Let us analyze the interaction part of the Hamiltonian of Eq. (17.14) denoted by H. Neglecting again the charge transfer terms, we write ... 

In the RVS analysis the charge transfer term ctX(a- B) is always corrected for basis set superposition error. 

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