Interaction energy component

Properties for the Optimized Complexes of Cytosine and Substituted Benzenes (Ph-X) Interaction Energy Components ... 

Details of the conformational energies of the ConA-ligand complexes are given in Table II. The difference in energy between the two binding modes for aMeMan in the binding site of ConA is due mainly to the difference in the interaction energy component. 

Contrary to the previously described supermolecular approach, perturbation theory treatment allows for the partition of the interaction energy into physically interpretable components. The most frequently used method for this purpose is symmetry-adapted perturbation theory (SAPT) [13]. More recently, great effort has also been invested in the development of DFT-SAPT [14-16], In the present contribution, we use the variational-perturbational scheme [17-20], In this approach, the intermolecular interaction energy components are determined based on the wave functions of the subsystems evaluated in the dimer-centered basis set. Thus, both interaction energy and its components are BSSE-free. More details about this scheme can be found elsewhere [21-23]. The total intermolecular interaction energy at the MP2 level of theory can be expressed as follows ... 

Fig. 20.2 Proportional representation of the intermolecular interaction energy components, calculated at the MP2/aug-cc-pVDZ level of theory, for stacked nucleic acid base complexes. Shown is the percentage contribution to the sum of all stabilizing terms...

K.M. Langner, W.A. Sokalski, J. Leszczynski, Intriguing relations of interaction energy components in stacked nucleic acids. J. Chem. Phys. 127, 111 102 (2007)... 

The interaction energy components calculated using ONIOM(MP2/6-31G(d) HF/6-31G(d)) ... 

The remainder of this section will be devoted to the discussion of computational methods of Van der Waals constants without prior knowledge of the interaction energy, and to other (possibly convergent) angular expansions of the interaction energy components. 

Although Eqs. (1-123) and (1-138) can be applied in practice to compute the Van der Waals constants C , these constants depend in a quite complicated way on the angles (a)A, cob,R). If these constants were computed from Eqs. (1-122) and (1-123), such calculations would have to be performed for each orientation of interacting molecules. Therefore, it is preferable to introduce the multipole expansions for the interaction energy components E t, E , and E, in a such a way that the whole angular dependence is separated. As shown in Ref. (161) for all intermolecular separations the th-order polarization correction E can... 

Figure 4. The system of coordinates and angular dependence of the interaction energy components in ArC02 at R=7.0 aQ A) at the SCF level of theory, B) at the correlated level of theory.

Figure 6. Angular dependence of various two-body interaction energy components in the cyclic planar H2O trimer at R=3.0 A.

As a second model potential we shall briefly discuss the PES for the water dimer. Analytical potentials developed from ab initio calculations have been available since the mid seventies, when Clementi and collaborators proposed their MCY potential [49], More recent calculations by dementi s group led to the development of the NCC surface, which also included many-body induction effects (see below) [50]. Both potentials were fitted to the total energy and therefore their individual energy components are not faithfully represented. For the purposes of the present discussion we will focus on another ab initio potential, which was designed primarily with the interaction energy components in mind by Millot and Stone [51]. This PES was obtained by applying the same philosophy as in the case of ArCC>2, i.e., both the template and calibration originate from the quantum chemical calculations, and are rooted in the perturbation theory of intermolecular forces. 

In this section we discuss the most important problems occurring when one wants to make quantitative calculations of the different interaction energy components. These components have been defined in the previous section for two molecules, denoted by A and B. We shall outline some practical methods for the calculation of pair interaction energies. 

In order to analyze the interaction energy component, the symmetry-adapted perturbation theory (SAPT) [12] calculations were performed. SAPT have been used to analyze the interaction energies in terms of electrostatic, induction, dispersion, and exchange interaction components. The SAPT interaction energy (Dint) has been analyzed up to the second-order symmetry adapted perturbation theory the electrostatic energy (Dekt) consisting of and... 

Despite the fact that the Kitaura Morokuma approach allows insight into the nature of interaction to be obtained, it has also a lot of limitations. One of the most important is that the binding energy and its components are not free of the basis set superposition error [39]. Another variation-perturbation scheme of the decomposition of the interaction energy was previously proposed [40]. The starting wave functions of the subsystems are obtained in this approach in the dimer-centered basis set (DCBS) hence, the following interaction energy components free of BSSE can be obtained ... 

One can see that for typical hydrogen bonds, O-H- -O and F-H- -O for dimer of water and the FH OCH2 complex, respectively, the electrostatic term is the most important attractive term. In all of these cases the electrostatic term outweighs the exchange term, and hence the first order interaction energy component is negative. This is again in line with conditions that the H-bond is predominantly an electrostatic interaction. Table 4 contains also the... 

Figure 11 presents the dependencies between the H- H intermolecular distance proton acceptor (acceptor is the negatively charged hydrogen atom) and the interaction energy components. 

In practical applications of the sapt approach to interactions of many-elect ron systems, one has to use the many-body version of sapt, which includes order-by-order the intramonomer correlation effects. The many-body SAPT is based on the partitioning of the total Hamiltonian as H = F+V+W, where the zeroth-order operator F = Fa + Fb is the sum of the Fock operators for the monomers A and B. The intermolecular interaction operator V = H — Ha — Hb is the difference between the Hamiltonians of interacting and noninteracting systems, and the intramonomer correlation operator W = Wa + Wb is the sum of the Moller-Plesset fluctuation potentials of the monomers Wx — Hx — Fx, X — A or B. The interaction operator V is taken in the non-expanded form, i.e., it is not approximated by the multipole expansion. The interaction energy components of Eq. (1) are now given in the form of a double perturbation series,... 

W. A. Sokalski, P C. Hariharan, and J. J. Kaufman, nt. J. Quantum Chem., Quantum Biol. Symp., 21, 645 (1987). Comparison of Ab Initio MODPOT Interaction Energy Components against Large Basis Set MBPT(4) Calculations for Nitromethane Dimer. 

Consecutive dissociation energies and interaction energy components (for the definition see paragraph 2) for conse tive clust of AtpH [681. Energies in kcal/mol. 

Figure 3. Comparison of cation-7r and cation-water interactions. Notice the distinct differences in the various interaction energy components as a result of changes in the nature of the cation and the 7i-system.

The empirical intermolecular force fields are in most cases built of terms that are in a close correspondence with the interaction energy components described above. One may say that such force fields are simplest possible implementations of the SAPT approach. The functional forms used are based on SAPT analysis of the asymptotic behavior of the components. The electrostatic interactions are usually approximated by interactions of fractional charges located on atoms in each monomer. In simplest cases, the induction effects are not included explicitly but some more sophisticated force fields use the classical polarization model. The dispersion forces are accounted for by hnear combinations of l/R ab terms where R b are interatomic distances and the exchange forces by either exponential or 1 terms. 

Parrish, R. M., and Sherrill, C. D. (2014). Spatial assignment of symmetry adapted perturbation theory interaction energy components The atomic SAPT partition, J. Chem. Phys. 141, p. 044115, doi 10.1063/1.4889855. 

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