Semiempirical vibrational and electronic structures of C₆₀ and C₇₀

Abstract

The electronic and vibrational structures of C,, and C,,, have been calculated at the PM3 semiempirical level. C, has a partially delocalized structure, while C,, has both a localized set and a delocalized set of MOs. As with AM1 and MNDO, PM3 predicts the heat of formation of C,, to be greater than that of C,,,, and that C,,, is the thermodynamically more stable species. Calculation of the normal modes was accelerated over 40 times by limited use of symmetry theory.

Excess Li ions in a small graphite cluster

“…As for the core electrons we consider the effective core potential for calculating the forces between two atoms, whose model function is optimized so as to reproduce the well-known behavior of many chemical molecules in the PM3 model functions. 13 A total energy is given by the sum of electronic energy of valence electrons and the core repulsion energy. Since the repulsion energy between two Li ions, which are located above the center of a hexagonal ring in the honeycomb lattice, is relatively large compared with the electrostatic potential of the host honeycomb lattice, Li atoms can easily move on graphite surfaces.…”

A disappearing act performed by magnesium: the nucleotide exchange mechanism of Ran GTPase by quantum mechanics/molecular mechanics studies

“…In the QM/ MM calculation the magnesium ion, GDP, Thr24 and four coordinating water molecules were treated by PM3 method [30,31]. The QM region was truncated to include the first coordination sphere of the divalent ion (Fig.…”

MSINDO parameterization for third-row main group elements

“…An important point is the range of application in terms of elements. Here, most methods start with the first-row elements C, N, and O, together with H 1, 6 -8 and extend the method to other first-row elements F, 6, 9, 10 B, 10,11 Be, 10,12 and Li. 10 Extensions to compounds often require modifications of the formalism and are particularly assisted by the inclusion of d orbitals.…”

“…These are covered mainly by SINDO1 from Sc to Zn. 23 Zn is also parameterized in PM3, 12 AM1, 24 and MNDO/d, 25 12,14,28 Most of these publications contain statistics about the performance of the accuracy compared to experiment. If semiempirical methods are compared, controversies may arise.…”

“…10 Extensions to compounds often require modifications of the formalism and are particularly assisted by the inclusion of d orbitals. 13,14 Second-row elements have been covered by the following works: Na 14,15 ; Mg 12,14,16 ; Al 6,14,16,17 ; Si 6,14,16,18 ; P 6,14,19,20 ; S 6,14,21,22 ; and Cl. 6,9,14,16 In the third row, d or-bitals are definitely needed for transition metal compounds.…”