Ability of the PM3 quantum‐mechanical method to model intermolecular hydrogen bonding between neutral molecules

Abstract

The PM3 semiempirical quantum-mechanical method was found to systematically describe intermolecular hydrogen bonding in small polar molecules. PM3 shows charge transfer from the donor to acceptor molecules on the order of 0.02-0.06 units of charge when strong hydrogen bonds are formed. The PM3 method is predictive; calculated hydrogen bond energies with an absolute magnitude greater than 2 kcal mol-' suggest that the global minimum is a hydrogen bonded complex; absolute energies less than 2 kcal mol-' imply that other van der Waals complexes are more stable. The geometries of the PM3 hydrogen bonded complexes agree with high-resolution spectroscopic observations, gas electron diffraction data, and high-level ab initio calculations. The main limitations in the PM3 method are the underestimation of hydrogen bond lengths by 0.1-0.2 for some systems and the underestimation of reliable experimental hydrogen bond energies by approximately 1-2 kcal mol-l. The PM3 method predicts that ammonia is a good hydrogen bond acceptor and a poor hydrogen donor when interacting with neutral molecules. Electronegativity differences between F, N, and 0 predict that donor strength follows the order F > 0 > N and acceptor strength follows the order N > 0 > F. In the calculations presented in this article, the PM3 method mirrors these electronegativity differences, predicting the F-H---N bond to be the strongest and the N-H---F bond the weakest. It appears that the PM3 Hamiltonian is able to model hydrogen bonding because of the reduction of two-center repulsive forces brought about by the parameterization of the Gaussian core-core interactions. The ability of the PM3 method to model intermolecular hydrogen bonding means reasonably accurate quantum-mechanical calculations can be applied to small biologic systems. 0 1993 by John Wiley & Sons, Inc.

The ability of the Gaussian‐2, Gaussian‐3, Complete Basis Set–QB3, and Complete Basis Set–APNO model chemistries to model the geometries of small water clusters

“…Xantheas [6] has reported a BLYP/aug-cc-pVDZ cyclic hexamer, with S 6 symmetry, with OOO distances of 2.714 Å and hydrogen bond angles of 179.1°. Losada [21] The PM3 method generally yields good geometries for hydrogen bonded systems such as water clusters [45][46][47], so it is a fair question to ask why with distances in Å and angles in degrees, for QCISD/ 6-311G* geometry optimized with CBS-APNO model chemistry, for B3LYP/6-311G(2d,d,p) geometry optimized with CBS-QB3 model chemistry, and for MP2(Full)/6-31G* geometry optimized with G2 and G3 model chemistries.…”

(Solid + liquid) equilibria, i.r., and semi-empirical studies of carbazole with selected tertiary amides

“…investigations rather than systematic ab initio studies was needed. Moreover, the PM3 method has been shown (26) to yield geometries different from those yielded by the AM1 method but consistent with both the high-resolution spectroscopy and the gas electron diffraction data and with high-level ab initio calculations. On the other hand, the AM1 method can, in some cases, yield strange bifurcated structures.…”

Linear free energy relationships of the 13C NMR chemical shifts in 5-(3- and 4-substituted arylazo)-4,6-dimethyl-3-cyano-2-pyridones

“…In our work we used the MNDO-PM6 method that proved to be highly reliable for investigating the molecular properties of molecules, ions, [21][22][23][24][25][26][27][28][29] and zwitterions. 30 The MOPAC program package, Version 7.01 was used.…”