Semi‐empirical calculations of molecular trajectories: Method and applications to some simple molecular systems

Stewart, James J. P.; Davis, Larry P.; Burggraf, Larry W.

doi:10.1002/jcc.540080808

Cited by 105 publications

(82 citation statements)

References 9 publications

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“…The MRCI wave function included all single and double excita-tions from the FORS reference space into the virtual space, referred to as MR͑SD͒-CI. 18,19 Dynamic reaction path ͑DRP͒ 24,25 calculations were used to examine the most probable reaction channels on the PES'. To verify the basis set convergence, most of the calculations, including geometry optimizations of all stationary points on the PES', were performed subsequently with the 6-311G*, 26 aug-cc-pVTZ, and aug-cc-pVQZ 27 basis sets.…”

Section: Methodsmentioning

confidence: 99%

Potential energy surfaces for the Al+O2 reaction

Pak

Gordon

2003

The Journal of Chemical Physics

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We present a systematic multiconfigurational study of the lowest two doublet potential energy surfaces of atomic aluminum with molecular oxygen. The most likely products, AlO and AlO2,are expected to figure prominently in subsequent reactions to form Al2O3. The main reaction pathways on both surfaces invariably lead to the formation of cyclic AlO2, possibly followed by isomerization to the lower-energy linear AlO2 isomer. A reaction path leading from Al+O2directly to AlO+O was not located. However, both AlO2 isomers can dissociate to AlO+Owith no barrier beyond endothermicity. There is also no barrier for the reaction of AlO2 with AlO to form Al2O3, and this reaction is highly exothermic. We present a systematic multiconfigurational study of the lowest two doublet potential energy surfaces of atomic aluminum with molecular oxygen. The most likely products, AlO and AlO 2 , are expected to figure prominently in subsequent reactions to form Al 2 O 3 . The main reaction pathways on both surfaces invariably lead to the formation of cyclic AlO 2 , possibly followed by isomerization to the lower-energy linear AlO 2 isomer. A reaction path leading from AlϩO 2 directly to AlOϩO was not located. However, both AlO 2 isomers can dissociate to AlOϩO with no barrier beyond endothermicity. There is also no barrier for the reaction of AlO 2 with AlO to form Al 2 O 3 , and this reaction is highly exothermic.

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Section: Methodsmentioning

confidence: 99%

Potential energy surfaces for the Al+O2 reaction

Pak

Gordon

2003

The Journal of Chemical Physics

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“…1 One representative approach is the direct dynamics method, [2][3][4][5] in which a classical trajectory is generated on-the-fly by using the potential energy and energy gradient evaluated through ab initio electronic structure calculations. The great advantage of this approach is that there are no requirements of potential energy functions in advance for dynamics calculations.…”

Section: Introductionmentioning

confidence: 99%

“…These contour plots illustrate a strong coupling between Q 1 and Q 3 . 8 It is valuable to reconsider the above discussions in terms of vibrational wave functions derived from direct VSCF/CCB(nMR) calculations using three different PESs, i.e., the harmonic potential ͑HA͒, ͑b͒ V (1) in CCB͑1MR͒, and ͑c͒ V (2) in CCB͑2MR͒. Figure 2 shows contour plots of those VSCF wave functions determined using direct VSCF/CCB(nMR) calculations for states ϭ(1,0,0) ( 1 (1) (Q 1 )ϫ 0 (3) (Q 3 )) and ϭ(0,0,1) ( 0 (1) (Q 1 )ϫ 1 (3) ϫ(Q 3 )), where in this notation, the superscript refers to the normal mode ͑1, 2, or 3͒, and i means the modal wave function for the ith vibrational state.…”

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confidence: 99%

Direct vibrational self-consistent field method: Applications to H2O and H2CO

Yagi

Taketsugu

Hirao

et al. 2000

The Journal of Chemical Physics

158

123

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The vibrational self-consistent field (VSCF) and virtual configuration interaction (VCI) methods are directly combined with ab initio electronic structure calculations for evaluations of the potential energy at VSCF quadrature points. Referred to as direct VSCF and direct VCI, respectively, these methods have been applied to evaluations of anharmonic vibrational energy levels of H2O and H2CO at the second-order Mo/ller-Plesset MP2/aug-cc-pVTZ and MP2/cc-pVTZ computational levels, respectively. The purpose of the present study is to develop a direct methodology for vibrational state calculations by examining the accuracy of the results, as well as their computational costs. In addition, the accuracy and applicability of two approximate potential energy surfaces (PES), a quartic force field (QFF), and the PES determined by the modified-Shepard interpolation method (Int-PES), are investigated via comparisons of calculated energy levels of vibrational states with those derived by the direct methods. The results are analyzed in terms of three considerations: (i) truncations of higher-order intercoordinate couplings in the PES; (ii) mode-mode coupling effects; (iii) approximations in ab initioelectronic structure methods. In the direct VCI calculations, the average absolute deviations in fundamental frequencies relative to the experimental values are 9.3 cm−1(H2O) and 34.7 cm−1(H2CO). The corresponding values evaluated with approximate PESs relative to those derived by the direct method are 35.0 cm −1 (QFF) and 15.3 cm −1 (Int-PES) for H2O, and 6.3 cm −1 (QFF) and 10.3 cm −1 (Int-PES) for H2CO. KeywordsVibrational states, Ab initio calculations, Ab initio electronic structure calculations, Configuration interaction, Electronic structure Disciplines Chemistry CommentsThe following article appeared The vibrational self-consistent field ͑VSCF͒ and virtual configuration interaction ͑VCI͒ methods are directly combined with ab initio electronic structure calculations for evaluations of the potential energy at VSCF quadrature points. Referred to as direct VSCF and direct VCI, respectively, these methods have been applied to evaluations of anharmonic vibrational energy levels of H 2 O and H 2 CO at the second-order Mo "ller-Plesset MP2/aug-cc-pVTZ and MP2/cc-pVTZ computational levels, respectively. The purpose of the present study is to develop a direct methodology for vibrational state calculations by examining the accuracy of the results, as well as their computational costs. In addition, the accuracy and applicability of two approximate potential energy surfaces ͑PES͒, a quartic force field ͑QFF͒, and the PES determined by the modified-Shepard interpolation method ͑Int-PES͒, are investigated via comparisons of calculated energy levels of vibrational states with those derived by the direct methods. The results are analyzed in terms of three considerations: ͑i͒ truncations of higher-order intercoordinate couplings in the PES; ͑ii͒ mode-mode coupling effects; ͑iii͒ approximations in ab initio electronic structure meth...

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“…All theoretical calculations were carried out by the semiempirical PM3 method with Spartan molecular modelingÅsoftwareÅ [15][16][17][18][19].ÅTheÅcandidateÅtransition-state structures and key structures on the potential energy surface were optimized. Heats of formation (in kcal/mol) of the optimized structures were calculated [16Å -18].ÅAllÅoptimizedÅstructuresÅwereÅsubjectedÅto vibrational frequency analysis.…”

Section: Methodsmentioning

confidence: 99%

Mass spectrometric studies of the gas phase retro-Michael type fragmentation reactions of 2-hydroxybenzyl-N-pyrimidinylamine derivatives

Wang

Zhang

Guo

et al. 2005

J. Am. Soc. Mass Spectrom.

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The gas-phase fragmentation reactions of 2-hydroxybenzyl-N-pyrimidinylamine derivatives (Compounds 1 to 6), the O-N-type acid-catalyzed Smiles rearrangement products of 2-pyrimidinyloxy-N-arylbenzylamine derivatives, have been examined via positive ion matrix-assisted laser desorption/ionization (MALDI) infrared multiphoton dissociation (IRMPD) mass spectrometry in FT-ICR MS and via negative ion electrospray ionization (ESI) in-source collisioninduced dissociation (CID) mass spectrometry, respectively. The major fragmentation pathway of protonated 1 to 6 gives the F ions under IRMPD; theoretical results show that the retro-Michael reaction channel is more favorable in both thermodynamics and kinetics. This explanation is supported by H/D exchange experiments and the MS/MS experiment of acetylated 1. Deprotonated 1 to 6 give rise to the solitary E ions (aromatic nitrogen anions) in the negative ion in-source CID; theoretical calculations show that a retro-Michael mechanism is more reasonable than a gas-phase intramolecular nucleophilic displacement (S N 2) mechanism to explain this reaction process. T andem mass spectrometry of either positive or negative ions not only provides extensive structural information for organic molecules [1, 2], especially for peptides and proteins [3][4][5], but can also act as an important gas-phase "physical organic" tool for mechanistic studies of organic chemistry [6 -8]. The solvent-free and unimolecular conditions in MS/MS make the gas-phase reactions different from the condensed phase analogous reactions; specifically, the gasphase chemistry may provide insight into some unique and intrinsic characteristics for the intramolecular organic reactions [9 -13]. Previous IRMPD mass spectrometric studies of protonated 2-pyrimidinyloxy-N-arylbenzyl amine derivatives reveal some gas-phase rearrangement reactions [14]. In particular, the gasphase S N Ar type rearrangement inspired us to investigate the rearrangement reaction of 2-pyrimidinyloxy-Narylbenzylamine derivatives in the condensed phase. The results show that the gas-phase S N Ar type rearrangement has solution phase analogs, the acid-catalyzed Smiles rearrangement reaction, which is summarized in Scheme 1. Six 2-hydroxybenzyl-Npyrimidinylamine derivatives (Compounds 1 to 6), the Smiles rearrangement products of 2-pyrimidinyloxy-Narylbenzylamine derivatives, are shown in Scheme 2.As an important chemical pathway of this kind of herbicide, a thorough understanding of the MS/MS and MS n data of these rearrangement products is important for bioactivity mechanisms, degradation pathways, and metabolism research. Analysis of the positive ion MALDI-IRMPD data from protonated 1 to 6 reveals that the F ions are main product ions. Two different mechanisms, an S N 2 or a retro-Michael reaction, are proposed to explain the formation pathway of F ions observed from positive ion MALDI-IRMPD of protonated 1 to 6. Theoretical calculations show that the retro-Michael mechanism is more reasonable.Compounds 1 to 6 have active phenol hydroxyl group...

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Semi‐empirical calculations of molecular trajectories: Method and applications to some simple molecular systems

Cited by 105 publications

References 9 publications

Potential energy surfaces for the Al+O2 reaction

Potential energy surfaces for the Al+O2 reaction

Direct vibrational self-consistent field method: Applications to H2O and H2CO

Mass spectrometric studies of the gas phase retro-Michael type fragmentation reactions of 2-hydroxybenzyl-N-pyrimidinylamine derivatives

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