Hartree-Fock electrostatic potentials

Levy, M., S. C. Clement, and Y. Tal. 1981. Correlation Energies from Hartree-Fock Electrostatic Potentials at Nuclei and Generation of Electrostatic Potentials from Asymptotic and Zero-Order Information. In Chemical Applications of Atomic and Molecular Electrostatic Potentials, P. Politzer, and D. G. Truhlar, Eds. Plenum Press, New York. 

We determined the coefficients in eqs. (17) and (18) by fitting to general databases of experimental AHvap and AHsub, using Hartree-Fock electrostatic potentials [13,14] however Rice et al reparametrized these equations at the B3LYP/6-31G level in terms of data pertaining specifically to energetic compounds [85]. Their average absolute deviations for AHvap and AHsub were 1.2 and 2.7 kcal/mole, respectively. 

In this work we have used this version of the mutually consistent field method (MCF) (48) which has been developed to treat the interactions between polymer chains (69). Each subsystem is computed in the potential field of the partner system. The Coulomb potentials of the elementary cell of one chain, represented by a point charge distribution which are fitted to the Hartree-Fock Coulomb potential are included in the one-electron part of the Fock matrix of the other chain and vice versa (for more details see Section 2.4). The procedure of taking into account the effect of the mutually polarization is repeated until consistent solutions are obtained for the charge distributions. Computing finally the interaction between these point charge representations, one obtains the electrostatic and the polarization energy contribution together. 

How does a rigorously calculated electrostatic potential depend upon the computational level at which was obtained p(r) Most ab initio calculations of V(r) for reasonably sized molecules are based on self-consistent field (SCF) or near Hartree-Fock wavefunctions and therefore do not reflect electron correlation in the computation of p(r). It is true that the availability of supercomputers and high-powered work stations has made post-Hartree-Fock calculations of V(r) (which include electron correlation) a realistic possibility even for molecules with 5 to 10 first-row atoms however, there is reason to believe that such computational levels are usually not necessary and not warranted. The Mpller-Plesset theorem states that properties computed from Hartree-Fock wave functions using one-electron operators, as is T(r), are correct through first order (Mpller and Plesset 1934) any errors are no more than second-order effects. 

It has been shown that the electrostatic potentials of formamide calculated at near-Hartree-Fock (HF/6-31G ) and post-Hartree-Fock (MP2/6-31G ) levels are qualitatively similar (Politzer and Murray 1991). Both computational approaches predict the oxygen to be the preferred site for electrophilic attack (Seminario, Murray, and Politzer 1991). It is further noteworthy that SCF results obtained with minimal basis sets (e.g., HF/STO-3G and HF/STO-5G) are also in good agreement with those calculated at the higher computational levels. 

The second term in Equation 1, , involves carrying out a Poisson-Boltzmann calculation and evaluating the exposed surface area of all atoms for all the snapshots for C, M, and L. Currently, we use Hartree-Fock (HF)/6-31G restrained electrostatic potential (RESP)13 charges and PARSE14 radii for the PB calculation within DELPHI15 and the program... 

Figure 1. Electrostatic potential on the molecular surface of dimethylnitrosamine, computed at the Hartree-Fock STO-5G //STO-3G level. Two views are presented the top shows the lone pair (purple color) on the amino nitrogen. Color ranges, in kcal/mole, are purple, more negative than -20 blue, between -20 and -10 green, between -10 and 0 yellow, between 0 and +13 red, more positive than +13.

The values of the ESP at the nuclear positions, as obtained from the electron and Hartree-Fock structure amplitudes for the mentioned crystals (using a K-model and corrected on self-potential) are given in table 2. An analysis shows that the experimental values of the ESP are near to the ab initio calculated values. However, both set of values in crystals differ from their analogs for the free atoms [5]. It was shown earlier (Schwarz M.E. Chem. Phys. Lett. 1970, 6, 631) that this difference in the electrostatic potentials in the nuclear positions correlates well with the binding energy of Is-electrons. So an ED-data in principle contains an information on the bonding in crystals, which is usually obtaining by photoelectron spectroscopy. 

The same geometries were also used to compute electrostatic potentials and local ionization energies, at the HF/6-31G level. Hartree-Fock F(r) and 7(r) are known to be quite satisfactory ... 

The penetration contribution to the electrostatic potential at R, is evaluated by application of the general expression of Eq. (8.49) for per for the spherical density (lt = ml = 0). The point-charge term, proportional to 1/Rfj-, must subsequently be subtracted. Due to the rapid decrease of the penetration terms with increasing R j, convergence is quickly achieved. For spherically averaged Hartree-Fock atom densities, inclusion of penetration terms for atoms within 10 A of the point under consideration is more than adequate. 

Exact solutions of the Schrddinger equation are, of course, impossible for atoms containing 90 electrons and more. The most common approximation used for solving Schrddinger s equation for heavy atoms is a Hartree-Fock or central field approximation. In this approximation, the individual electrostatic repulsion between the electron i and the N-1 others is replaced by a mean central field giving rise to a spherically symmetric potential... 

Atomic charges on the guest molecules were obtained from first principles Hartree-Fock calculations, fitting the electrostatic potential surface (EPS), then scaled up or down in order to reproduce the experimental dipole moments. Table 2 gives partial charges of typical molecules considered in our work. 

Figure 9. Electrostatic potential results for L-asparagine H20 in the OCN plane A, X-Ray, B, Hartree-Fock/6-31G, contours from -0.02 to 0.85 e(47ce0a0) 1. C, graph showing correlation between experimental p(r) and Hartree-Fock/ 6-31G results slope = 1.02, R2 = 0.973.

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