Quasiclassical simulations

Castillo, J. F., Hartke, B., Werner, H.-J., Aoiz, F. J., Banares, B. and Martinez-Haya, B. (1998) Quaiinim mechanical and quasiclassical simulations of molecular beam experiments for the F+H2—>HF+H reaction on two ab intio potential energy surfaces, J. Chem. Phys. 109, 7224-37. 

In a mixed quantum-classical simulation such as a mean-field-trajectory or a surface-hopping calculation, the population probability of the diabatic state v[/ t) is given as the quasiclassical average over the squared modulus of the diabatic electronic coefficients dk t) defined in Eq. (27). This yields... 

When potential surfaces are available, quasiclassical trajectory calculations (first introduced by Karplus, et al.496) become possible. Such calculations are the theorist s analogue of experiments and have been quite successful in simulating molecular reactive collisions.497 Opacity functions, excitation functions, and thermally averaged rate coefficients may be computed using such treatments. Since initial conditions may be varied in these calculations, state-to-state cross sections can be obtained, and problems such as vibrational specificity in the energy release of an exoergic reaction and vibrational selectivity in the energy requirement of an endo-... 

Direct dynamics calculations were carried out with quasiclassical normalmode sampling from a canonical ensemble at 923 K (the experimental reaction temperature). Simulations initiated at the vicinity of TS for rearrangement of carbene 13 to 14 via oxirene 12, and 300 trajectories were obtained at DFT methods. The preliminary results reported in the manuscript showed that preferred formation of 15a over 15b by the ratio of 1.8 7.6 depends on the method used. The results were qualitatively consistent with the value of 2.5 deduced from the experiment. The non-unity ratio likely arises from the situation that two methyl groups in 14 are dynamically unequal on the carbene formation process. 

Figure 7 A comparison of dissociation probabilities obtained from six-dimensional classical and quantum dynamics simulations for the H2/Cu(l 0 0) system [57]. There is good agreement between quantum and quasiclassical (for which hie molecule has initial vibrational energy equal to that of the quantum state) results.

In addition, the dynamics of the reverse reactions (-2) and (-3) were investigated using a similar method. In this case translationally excited OH radicals were generated by laser photolysis of H2O2 and the H atoms produced in the reactions were detected by means of VUV-LIF at the Lyman-a-transition. We will compare the experimental results with results from dynamical simulations e.g. quasiclassical trajectory (QCT) calculations and - if possible - with the results obtained by applying quantum scattering (QMS) methods. 

Another valuable use of accurate quantum dynamics calculations is testing the validity of classical simulations for predicting product-state distributions, and reduced-dimensionality studies of this issue are available for both Cl + H2 [67] and H + CI2 [104], In the present case extensive quasiclassical trajectory (( CT) calculations have been carried out for the full-dimensional Cl + D2 reaction by Aoiz and Bahares [105]. An example of how the QCT results compare to the accurate quantum ones is given in Fig. 4, which shows differential cross sections for Cl + D2(v=0J=1) —> DCl(v ) + D, where v and v are initial and final vibrational quantum number, respectively, j is initial rotational quantum number, and the results are summed over final rotational quantum number j. The comparison in Fig. 4 is for an initial relative translational energy of 10.1 kcal. The agreement is quite good. Notice, however, that the QCT method overestimates the amount of vibrationally excited product. 

Sun L, Base WL (2010) Comparisons of classical and Wigner sampling of transition state energy levels for quasiclassical trajectory chemical dynamics simulations. J Chem Phys 133 044313... 

Martinez-Nunez E, Femandez-Ramos A, Vazquez SA, Marques JMC, Xue M, Base WL (2005) Quasiclassical dynamics simulation of the collision-induced dissociation of CrfCQ) with Xe. J Chem Phys 123 154311... 

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