Molecular orbital treatments of hydrogen bonded systems. 2. Dimers of water and HCN

Calculations were performed to investigate the reliabilities of the CNDO/2, PRDDO, and MNDO approximate molecular orbital methods. Systems selected for study included the linear, cyclic, and bifurcated dimers of water as well as the linear and cyclic dimers of HCN. The PRDDO method was found to provide the most consistently accurate reproduction of ab initio and experimental data. CNDO/2 performed fairly well in a number of cases but yielded extremely poor results for the cyclic dimers of both H₂O and HCN. Hydrogen bond strengths were consistently underestimated by MNDO which also furnished erroneously large intermolecular separations. In addition, MNDO calculations indicate the bifurcated water dimer to be most stable in contrast to other quantum mechanical and experimental information.See Ref. [1] for Paper 1 of this series.     

Accurate molecular electrostatic potentials based on modified PRDDO/M wave functions: II. Electrostatic potentials inside the molecular van der Waals envelope

In part I of this series, the PESP (parameterized electrostatic potential) method was described and applied to the calculation of electrostatic-potential-derived charges for a wide variety of organic and inorganic systems. Based on PRDDO/M wave functions and parameterized against ab initio MP2/6-31G** calculations, PESP is an order of magnitude faster than ab initio STO-3G calculations, while achieving a level of accuracy that rivals that of far more sophisticated ab initio methods. In this study, the application of the PESP method to the high potential regions of molecules containing H, C, N, O, F, P, S, Cl, and Br is described. For a collection of 48 molecules and 55 distinct lone pair minima, PESP yields the location and depth of lone pair minima to an average accuracy (relative to MP2/6-31G**) of 0.03 Å and 2.5 kcal/mol, respectively. Similarly, the location and well depths of minima in the π regions of organic molecules are calculated to an accuracy of 0.08 Å and 1.5 kcal/mol. PESP electrostatic potential maps are, in some cases, virtually indistinguishable from those obtained at the MP2/6-31G** level. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1682–1693, 1997     

Accurate molecular electrostatic potentials based on modified PRDDO/M wave functions: III. Extension of the PESP method for calculation of electrostatic potential-derived atomic charges to compounds containing Li+, Na+, Mg2+, K+, Ca2+, Zn2+, and I

The PESP (Parameterized ElectroStatic Potential) method for calculating molecular electrostatic potentials, previously parameterized for H, C, N, O, F, P, S, Cl, and Br, is extended to molecules containing Li⁺, Na⁺, Mg²⁺, K⁺, Ca²⁺, Zn²⁺, and I. For a collection of 166 molecules containing 1668 atoms with at least one metal or iodine atom, PESP achieves an average absolute deviation in electrostatic potential-derived atomic charges of 0.042e⁻ compared with ab initio MP2/6-31G** calculations, with a correlation coefficient of 0.996. For a larger data set, consisting of 311 molecules encompassing all of the 16 elements just listed (2488 total atoms), PESP achieves an average absolute deviation of 0.040e⁻ and a correlation coefficient of 0.995. PESP calculations are an order of magnitude faster than the simplest ab initio method (STO-3G) on large molecules, while achieving a level of accuracy that rivals much more elaborate ab initio methods. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1456–1469, 1998     

Accurate molecular electrostatic potentials based on modified PRDDO/M wave functions. I. Electrostatic potential derived atomic charges

A new approach for the calculation of electrostatic potential derived atomic charges is presented. Based on molecular orbital calculations in the PRDDO/M approximation, the new parametrized electrostatic potential (PESP) method is parametrized against ab initio MP2/6-31G** calculations. For a data set of 820 atoms in 145 molecules containing H, C, N. O, F, P, S, Cl, and Br (including hypervalent species), the PESP method achieves a mean absolute error of 0.037 e⁻ with a correlation coefficient of 0.990. Unlike other approximate approaches, no scaling factor is required to improve the agreement between PESP charges and the underlying ab initio results. PESP calculations are an order of magnitude faster than the simplest ab initio calculation (STO-3G) on large molecules while achieving a level of accuracy that rivals much more elaborate ab initio methods. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 955–969, 1997