Analysis of the core-repulsion functions used in AM1 and PM3 semiempirical calculations: Conformational analysis of ring systems

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Abstract

The AM1 and PM3 potential energy surfaces of cyclopentane have been compared and the energy difference between two (boat and chair) cyclohexane conformers analyzed. The effects of reparameterization and different core-repulsion functions (CRFs) have been studied. The H-H, C-H, and C-C CRF energy con- tributions have been calculated separately. The results show that the CRF energy corrections stabilize the correct (MM2 and ab initio) geometries. The PM3 equilibrium geometry of cyclopentane is closer to the MM2 and ab initio results than the AM1 geometry. It is known that above 190 pm the AM1 H-H CRF curve is smooth and negative but the PM3 H-H CRF curve has a trough and a shoulder. It has been shown that this latter oscillation is not damped by other parameters. As a result, the H-H PM3 energy gradient curve is different from the quasilinear AM1 and ab initio gradient curves.

Original languageEnglish
Pages (from-to)895-898
Number of pages4
JournalJournal of Computational Chemistry
Volume14
Issue number8
Publication statusPublished - Aug 1 1993

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Ring
Curve
Cyclopentanes
Energy Function
Geometry
Gradient
Potential Energy Surface
Reparameterization
p.m.
Energy
Potential energy surfaces
Damped
Boats
Cyclohexane
Oscillation

ASJC Scopus subject areas

  • Chemistry(all)
  • Computational Mathematics

Cite this

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title = "Analysis of the core-repulsion functions used in AM1 and PM3 semiempirical calculations: Conformational analysis of ring systems",
abstract = "The AM1 and PM3 potential energy surfaces of cyclopentane have been compared and the energy difference between two (boat and chair) cyclohexane conformers analyzed. The effects of reparameterization and different core-repulsion functions (CRFs) have been studied. The H-H, C-H, and C-C CRF energy con- tributions have been calculated separately. The results show that the CRF energy corrections stabilize the correct (MM2 and ab initio) geometries. The PM3 equilibrium geometry of cyclopentane is closer to the MM2 and ab initio results than the AM1 geometry. It is known that above 190 pm the AM1 H-H CRF curve is smooth and negative but the PM3 H-H CRF curve has a trough and a shoulder. It has been shown that this latter oscillation is not damped by other parameters. As a result, the H-H PM3 energy gradient curve is different from the quasilinear AM1 and ab initio gradient curves.",
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T2 - Conformational analysis of ring systems

AU - Csonka, G.

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N2 - The AM1 and PM3 potential energy surfaces of cyclopentane have been compared and the energy difference between two (boat and chair) cyclohexane conformers analyzed. The effects of reparameterization and different core-repulsion functions (CRFs) have been studied. The H-H, C-H, and C-C CRF energy con- tributions have been calculated separately. The results show that the CRF energy corrections stabilize the correct (MM2 and ab initio) geometries. The PM3 equilibrium geometry of cyclopentane is closer to the MM2 and ab initio results than the AM1 geometry. It is known that above 190 pm the AM1 H-H CRF curve is smooth and negative but the PM3 H-H CRF curve has a trough and a shoulder. It has been shown that this latter oscillation is not damped by other parameters. As a result, the H-H PM3 energy gradient curve is different from the quasilinear AM1 and ab initio gradient curves.

AB - The AM1 and PM3 potential energy surfaces of cyclopentane have been compared and the energy difference between two (boat and chair) cyclohexane conformers analyzed. The effects of reparameterization and different core-repulsion functions (CRFs) have been studied. The H-H, C-H, and C-C CRF energy con- tributions have been calculated separately. The results show that the CRF energy corrections stabilize the correct (MM2 and ab initio) geometries. The PM3 equilibrium geometry of cyclopentane is closer to the MM2 and ab initio results than the AM1 geometry. It is known that above 190 pm the AM1 H-H CRF curve is smooth and negative but the PM3 H-H CRF curve has a trough and a shoulder. It has been shown that this latter oscillation is not damped by other parameters. As a result, the H-H PM3 energy gradient curve is different from the quasilinear AM1 and ab initio gradient curves.

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