Electrostatic Potential, Computation

The macroscopic property of interest, e.g., heat of vaporization, is represented in terms of some subset of the computed quantities on the right side of Eq. (3.7). The latter are measures of various aspects of a molecule s interactive behavior, with all but surface area being defined in terms of the electrostatic potential computed on the molecular surface. Vs max and Fs min, the most positive and most negative values of V(r) on the surface, are site-specific they indicate the tendencies and most favorable locations for nucleophilic and electrophilic interactions. In contrast, II, a ot and v are statistically-based global quantities, which are defined in terms of the entire molecular surface. II is a measure of local polarity, °fot indicates the degree of variability of the potential on the surface, and v is a measure of the electrostatic balance between the positive and negative regions of V(r) (Murray et al. 1994 Murray and Politzer 1994). 

Kireev, D.B., Fetisov, V.I. and Zefirov, N.S. (1994). Approximate Molecular Electrostatic Potential Computations. Applications to Quantitative Structure-Activity Relationships. J.Mol. Struct. (Theochem), 110,143-150. 

Figure 1. Electrostatic potentials, computed at the Hartree-Fock STO-5G//STO-3G level, on the front and back molecular surfaces of the three nitroheterocycles shown. Their measured impact sensitivities, taken from Storm et al [3], are indicated. Color ranges, in kcal/mole red, more positive than 40 yellow, between 40 and 20 green, between 20 and 0 blue, between 0 and -20 violet, more negative than -40.

Fig. 3 Calculated electrostatic potential computed on the 0.001 electrons/Bohr contour of the electron density in SF2 and Se(CN)2- Both molecules show two equivalent o-holes (in red) approximately located on the extensions of the covalent bonds, F-S (left) and C-Se (right)...

Finally the differences between the electrostatic potential computed by using the various shapes of cavity considered above appear to lie within the error bars of the Monte-Carlo computation so that an ellipsoidal cavity appears to be an acceptable first approximation. 

Statistically Based Interaction Indices Derived from Electrostatic Potentials Computed on Molecular Surfaces... 

Cox S R and D E Williams 1981. Representation of the Molecular Electrostatic Potential by a New Atomic Charge Model. Journal of Computational Chemistry 2 304-323. 

Ferenczy G G, C A Reynolds and W G Richards 1990. Semi-Empirical AMI Electrostatic Potentials and AMI Electrostatic Potential Derived Charges - A Comparison with Ah Initio Values. Journal of Computational Chemistry 11 159-169. 

Kurst G R, R A Stephens and R W Phippen 1990. Computer Simulation Studies of Anisotropic iystems XIX. Mesophases Formed by the Gay-Berne Model Mesogen. Liquid Crystals 8 451-464. e F J, F Has and M Orozco 1990. Comparative Study of the Molecular Electrostatic Potential Ibtained from Different Wavefunctions - Reliability of the Semi-Empirical MNDO Wavefunction. oumal of Computational Chemistry 11 416-430. 

Price S L, R J Harrison and M F Guest 1989. An Ab Initio Distributed Multipole Study of the Electrostatic Potential Around an Undecapeptide Cyclosporin Derivative and a Comparison with Point Charge Electrostatic Models. Journal of Computational Chemistry 10 552-567. 

M. P. Allen, D. J. Tildesley, Computer Simulation of Liquids Oxford, Oxford (1987). Chemical Applications of Atomic and Molecular Electrostatic Potentials P. Politzer, D. G. Truhlar, Eds., Plenum, New York (1981). 

Once the molecules are aligned, a molecular field is computed on a grid of points in space around the molecule. This field must provide a description of how each molecule will tend to bind in the active site. Field descriptors typically consist of a sum of one or more spatial properties, such as steric factors, van der Waals parameters, or the electrostatic potential. The choice of grid points will also affect the quality of the final results. 

Crystal can compute a number of properties, such as Mulliken population analysis, electron density, multipoles. X-ray structure factors, electrostatic potential, band structures, Fermi contact densities, hyperfine tensors, DOS, electron momentum distribution, and Compton profiles. 

Wave functions can be visualized as the total electron density, orbital densities, electrostatic potential, atomic densities, or the Laplacian of the electron density. The program computes the data from the basis functions and molecular orbital coefficients. Thus, it does not need a large amount of disk space to store data, but the computation can be time-consuming. Molden can also compute electrostatic charges from the wave function. Several visualization modes are available, including contour plots, three-dimensional isosurfaces, and data slices. 

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