Efficient microcanonical sampling

Trajectories were initiated by generating initial conditions with the efficient microcanonical sampling or quasiclassical normal-mode sampling procedures at 54.6 or 146.0 kcalmoC1 of vibrational energy for trimethylene. Trimethylene was then placed in the center of a box, with periodic boundary conditions, and surrounded by an argon bath with an equilibrium temperature and density. Initially, trimethylene was in a nonequilibrium state with respect to the bath, since its coordinates and momenta were held fixed while the bath was equilibrated, and the trajectories were propagated until either cyclopropane or propene was formed. 

G. Nyman, S. Nordholm, and H. W. Schranz, J. Chem. Phys., 93, 6767 (1990). Efficient Microcanonical Sampling for a Selected Total Angular Momentum. Applications to HO and HjO. H. W. Schranz, S. Nordholm, and G. Nyman,/. Chem. Phys., 94,1487 (1991). An Efficient Microcanonical Sampling Procedure for Molecular Systems. H. W. Schranz, /. Phys. Chem., 95, 4581 (1991). On the Microcanonical Weight Function. 

Decomposition of methyl nitrite by concerted elimination (CH2O and HNO formation) and O-N bond dissociation (CH3O and NO formation) has been investigated by classical trajectories and statistical variational efficient microcanonical sampling-transition state theory. The dissociation, which exhibits an inverse deuterium isotope effect, is markedly faster than the four-centre elimination process. The UHF/AMl MO method has been used to study thermolyses of aroyl nitrites. ... 

Other algorithms have been developed for speeding up the uniform sampling of phase space points. For example, the efficient microcanonical sampling series of schemes exploits the possibility of sampling independently the spatial coordinates and momenta, simply by weighting the sampled geometries by their associated momentum space density. 

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