Electrostatic embedding

Cisneros GA, Piquemal J-P, Darden TA (2006) QM/MM electrostatic embedding with continuous and discrete functions. J Phys Chem B 110 13682... 

The electrostatic embedding method is included in numerous quantum chemistry packages and although quantum chemical computations using this technique are straightforward, some difficulties in its application in the context of QM/MM approaches are encountered (27,34). The main problems are associated with the derivation of forces in a periodic environment which has to be employed to ensure that the system reflects the bulk of a liquid. 

This electrostatic embedding strategy has been successfully applied in a variety of QMCF MD simulations of hydrated systems (38 3). The embedding technique in connection with improvements of the QM/MM coupling leads to a significantly increased accuracy of the description of the systems compared to conventional QM/MM MD procedures. The QMCF framework is compatible with any affordable quantum chemical level and will enable the application of correlated ab initio methods (e.g., MP/2) in the near future. 

The description of the perturbation induced by the medium through a suitable external electric field (i.e. an electrostatic embedding scheme). 

The electrostatic embedding approach appears reasonable in cases of weak interactions, with negligible intermolecular charge transfer, provided that the interactions can be described as some average electric perturbation. By properly modifying the disposition of the point charges more realistic embedding schemes could also be introduced. 

These three critical points, namely the neglect of non-Coulombic contributions for solute atoms, a fluctuating charge distribution of the QM particles and electrostatic embedding of MM partial charges, lead to the formulation of the quantum mechanical charge field (QMCF) ansatz [54] which has been applied in molecular dynamics studies of various hydrated systems, recently. 

The electrostatic embedding of MM partial charges as a perturbational potential in the Hamilton operator is a frequently used method to account for Coulombic interactions between QM atoms and MM point charges. As the respective potential contributions influence the quantum mechanical calculation and by that the molecular orbitals and the associated electron density, this approach is rated superior compared to a Coulombic interaction model utilising fixed partial charges. 

Addressing large molecular systems is the aim of Chapter 3, which reviews a recently developed model based on the combined use of quantum mechanics and molecular mechanics (QM/MM). This approach uses a fully self-consistent polarizable embedding (PE) scheme described in the paper. The PE model is generally compatible with any quantum chemical method, but this review is focused on its combination with density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The PE method is based on the use of an electrostatic embedding potential resulting from the permanent charge distribution of the classically treated part of... 

The simplest and the most commonly used form of the coupling term comprises only electrostatic components (electrostatic embedding). It has been combined with Kohn-Sham calculations as well as with wave-function based methods. In the electrostatic embedding, only the first two components of the whole embedding poten-... 

Dahlke, E. E., and Truhlar, D. G. (2007). Electrostatically embedded many-body correlation energy, with applications to the calculation of accurate second-order M0ller-Plesset perturbation theory energies for large water clusters,/. Chem. Theory Comput. 3(4), 1342-1348. 

Alvarez-Ibarra A, Koester A, Zhang R, Salahub DR (2012), Asymptotic Expansion for Electrostatic Embedding Integrals in QM/MM Calculations. J Chem Theor Comp DOI 10.1021/ct300609z... 

Kastner J, Thiel S, Senn HM, Sherwood P, Thiel W (2007) Exploiting QM/MM capabilities in geometry optimizatirai a microiterative approach using electrostatic embedding. J Chem Theory Comput 3 1064... 

Another drawback of the QM/MM approach in its electrostatic embedding formulation is the fact that the MS system indeed is polarized by the presence of the environment through the term, but the multipoles... 

Higashi M, Truhiar DG (2008) Electrostatically embedded multiconfiguration molecular mechanics based on the combined density functional and molecular mechanical method. J Chem Theory Comput 4 790-803... 

Electrostatic embedding In the case of ionic compounds, the largest contribution to the potential exerted by the rest of the crystal on the (central region of the) cluster is due to long-range electrostatic interactions. These are accurately represented by the point charge approximation, that is, the Madelung potential ... 

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