Atomic charges RESP

Z1, P Cieplak, W D Cornell and P A Kolhnan 1993. A Well-Behaved Electrostatic Potential Based 5thod for Deriving Atomic Charges - The RESP Model. Journal of Physical Chemistry 97 10269-10280. sen H C, J P M Postma, W F van Gunsteren and J Hermans 1981. Interaction Models for Water in lation to Protein Hydration. In Pullman B (Editor). Intermolecular Forces. Dordrecht, Reidel, I. 331-342. 

The application of any xr-matrix also influences the distribution of the formal electrical charge of each atom (localized) resp. DE-system (delocalized). The monitoring of thoses changes during the sucessive applications of the B- and D-functions is done automatically according to the following principles. 

Well-Behaved Electrostatic Potential Based Method Using Charge Restraints for Deriving Atomic Charges The RESP Model. 

Bayly, C. I. Cieplak, P. Cornell, W. D. Kollman, P. A., A well-behaved electrostatic potential based method using charge restraints for deriving atomic charges the RESP model,. /. Phys. Chem. 1993, 97, 10269-10280... 

We now discuss a recently developed method to derive atomic charges from WFCs [225]. This method is closely related to the D-RESP procedure of the Roethlisberger group [226]. We consider a molecule of M atoms with charges Za and atomic positions R. The electronic distribution of the molecule is described by n WFCs with charges — at positions r. has a value of one for the spin polarized case and a value of two for spin restricted calculations. The electrostatic potential of the molecule derived from the WFCs is defined as... 

Bayly C1, P Cieplak, W D Cornell and P A Kollman 1993. A Well-Behaved Electrostatic Potential Based Method for Deriving Atomic Charges - The RESP Model. Journal of Physical Chemistry 97 10269-10280. 

C. I. Bayly, P. Cieplak, W. D. Cornell, and P. A. Kollman, J. Phys. Chem., 97,10269 (1993). A Well-Behaved Electrostatic Potential Based Method Using Charge Restraints for Deriving Atomic Charges The RESP Model. 

Direct comparison of force fields to benchmark-quality CCSD(T) energies is complicated by the fact that most standard, workhorse force fields do not include polarization terms. This leads to errors, but these errors can be partially compensated by other errors. Hence, a force field that compares poorly to CCSD(T) benchmarks for a set of van der Waals dimers may still perform fairly well for condensed-phase properties, due to error cancellation. This is the rationale for obtaining atomic charges in the AMBER force field using restrained electrostatic potential (RESP) fitting (Bayly, 1993) to modest-quality Hartree-Fock/6-31G quantum chemical computations this method tends to overestimate dipole moments, but this is considered beneficial for simulations in water, to approximately cancel errors from neglecting polarization effects... 

In RESP fit, restraint that keeps the atomic charge near zero are applied to each atom with a uniform weighting factor. In this fitting method, different weighting factors are assigned to the atoms, which are reversely proportional to the square of the base charges. 

The conformational search was performed with the module implemented in Hyperchem 7 [24] the geometry optimization, frequency analysis, and torsional barriers scan were done with the program suite Gaussian 09 [25] the RESP atomic charges were evaluated with the corresponding subroutine in the package Amber 8 [26]. The MD simulations were carried out with Amber 8. 

Another important ingredient of the force field is the parametrized atomic charges necessary for estimation of the electrostatic interactions. The mean RESP atomic charges obtained from the multiconformational fit of the electrostatic potential of the studied molecules in vacuum and in water are collected in Fig. 26.7. 

Fig. 26.7 RESP atomic charges of the non-hydrogen atoms obtained from fitting of the HF/6-31G electrostatic potential generated in vacuum (top) and in water (bottom)...

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... 

If separate D-RESP charge sets are fitted for every single one of the 36 frames, the standard deviation of the electrostatic field generated varies between 3.5 and 5% with respect to the full quantum reference. This accuracy is the best (in the least-squares sense) that can be obtained if the system is modeled with time-dependent atomic point-charges and represents the accuracy limit for a fluctuating point charge model of the dipeptide. 

Tab. 1.3 Comparison between different sets of atomic point charges for a zwitterionic Gly-Ala dipeptide in aqueous solution. D-RESP electrostatic potential derived charges [12] fitted to all 36 configurations. Hirshfeld average value of the Hirshfeld charges [89c] along the full trajectory, Amber AMBER 1995 force field [86], Gromos GROMOS96 force field [85], The charges of equivalent atoms are imposed to be equal.

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