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Theoretical investigation of the dissociation dynamics of vibrationally excited vinyl bromide on an ab initio potential-energy surface obtained using modified novelty sampling and feedforward neural networks. II. Numerical application of the method
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10.1063/1.2768948
/content/aip/journal/jcp/127/13/10.1063/1.2768948
http://aip.metastore.ingenta.com/content/aip/journal/jcp/127/13/10.1063/1.2768948

Figures

Image of FIG. 1.
FIG. 1.

Atom numbering used to define the interparticle distances.

Image of FIG. 2.
FIG. 2.

Illustration of the first cycle of the iterative novelty sampling procedure. The shaded distribution is the modified minimum distance distribution (see Ref. 1) of the 14 854 points obtained from the trajectories on the empirical potential surface. The unshaded histogram shows the distribution of minimum modified distances for the 19 821 new configurations from those in the shaded distribution. The new configurations are obtained in the first cycle of novelty sampling using a 15-140-1 NN fitted to the original 14 854 points. The failure of the two distributions to cover the same region of scaled minimum distances shows that there is not yet a sufficient sampling of configuration space to adequately represent the vinyl bromide potential surface.

Image of FIG. 3.
FIG. 3.

Illustration of the final cycle of the iterative novelty sampling procedure. The shaded distribution is the modified minimum distance distribution (see Ref. 1) of the 71 969 points obtained in the fourth cycle of the iterative procedure. The unshaded histogram shows the distribution of minimum modified distances for the new configurations from those in the shaded distribution. The new configurations are obtained in the fifth cycle of novelty sampling using a 15-140-1 NN fitted to the 71 969 points in the shaded distribution. As can be seen, the two distributions now span essentially the same region of scaled minimum distances. This is the novelty sampling criterion for convergence.

Image of FIG. 4.
FIG. 4.

Comparison of the output from the 15-140-1 NN for the 64 773 configurations in the training set with ab initio energies computed using MP4(SDQ) methods and the basis set described in the text. If the fit was perfect, all points would lie on a 45° line. The average absolute deviation is . The energy zero is taken to be the atoms of vinyl bromide when separated at infinite distance.

Image of FIG. 5.
FIG. 5.

Comparison of the output from the 15-140-1 NN for the 7196 configurations in the testing set with ab initio energies computed using MP4(SDQ) methods and the basis set described in the text. If the fit was perfect, all points would lie on a 45° line. The average absolute deviation is . The energy zero is taken to be the atoms of vinyl bromide when separated at infinite distance.

Image of FIG. 6.
FIG. 6.

Histogram showing the distribution of the deviations of the predicted energies obtained from the 15-140-1 NN and those resulting from electronic structure calculations at MP4(SDQ) level using the basis set described in the text. The results for all 71 969 configurations are included in the histogram. The energy zero is taken to be the atoms of vinyl bromide when separated at infinite distance.

Image of FIG. 7.
FIG. 7.

Computed decay curve for vinyl bromide at internal excitation randomly distributed over all 12 vibrational degrees of freedom. The line is a least-squares fit to the data. Its slope yields a total decay rate coefficient of .

Image of FIG. 8.
FIG. 8.

Distribution of vibrational energy in HBr subsequent to three-center dissociation. The points are the results obtained from 320 trajectories. The curve is a least-squares fit of a Boltzmann distribution. This fit corresponds to a HBr vibrational temperature of , which is in very good accord with the experimentally reported result in Ref. 24 of .

Tables

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Table I.

Configurations stored in each cycle of the iterative, novelty sampling process.

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Table II.

Range of input and target output variables for the 15-140-1 neural network. The atom numbers for the input bond distances are given in Fig. 6.

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Table III.

Comparison of predicted potential-energy barrier heights for three-center HBr and dissociation reactions.

Generic image for table
Table IV.

Comparison of harmonic vibrational frequencies for vinyl bromide obtained from MP4(SDQ) and MP2 calculations with results from a previously reported analytic surface and experiment. The frequencies are reported in equivalent wave numbers.

Generic image for table
Table V.

Branching ratios on the ab initio NN potential and an analytic potential surface at internal excitation energy.

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/content/aip/journal/jcp/127/13/10.1063/1.2768948
2007-10-04
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Theoretical investigation of the dissociation dynamics of vibrationally excited vinyl bromide on an ab initio potential-energy surface obtained using modified novelty sampling and feedforward neural networks. II. Numerical application of the method
http://aip.metastore.ingenta.com/content/aip/journal/jcp/127/13/10.1063/1.2768948
10.1063/1.2768948
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