An efficient microcanonical sampling procedure for molecular systems

A theory that describes the non-RRKM ͑non-Rice-Ramsperger-Kassel-Marcus͒ effects in the lifetime statistics of activated ozone molecules is derived. The non-RRKM effects are shown to originate due to the diffusive energy exchange between vibrational and rotational degrees of freedom in ozone molecule. The lifetime statistics is found to be intramolecular diffusion controlled at long times. The theoretical results are in good agreement with the direct MD simulations of lifetime statistics.

Section: The Rate Of Dissociation R"k…mentioning

confidence: 99%

Coriolis coupling as a source of non-RRKM effects in ozone molecule: Lifetime statistics of vibrationally excited ozone molecules

Kryvohuz

Marcus

2010

“…Notice that ͓E − V͑q͔͒ ͑3n−5͒/2 is the appropriate configuration weight for an isolated molecule composed by n atoms as obtained by factorizing out the contribution due to the center of mass motion in the way suggested by Schranz et al 23 An alternative form for Eq. ͑6͒ is obtained by using the Heaviside function H Ͼ ͑ṙ IRC ͒ selecting velocities directed from R to P and by rewriting the integral ratio as a product of two ratios 084108-3 Theory of atomic cluster dissociation J. Chem.…”

Section: ͑4͒mentioning

confidence: 99%

On possible simplifications in the theoretical description of gas phase atomic cluster dissociation

Mella¹

2009

In this work, we investigate the possibility of describing gas phase atomic cluster dissociation by means of variational transition state theory ͑vTST͒ in the microcanonical ensemble. A particular emphasis is placed on benchmarking the accuracy of vTST in predicting the dissociation rate and kinetic energy release of a fragmentation event as a function of the cluster size and internal energy. The results for three Lennard-Jones clusters ͑LJ n , n =8,14,19͒ indicate that variational transition state theory is capable of providing results of accuracy comparable to molecular dynamics simulations at a reduced computational cost. Possible simplifications of the master equation formalism used to model a dissociation cascade are also suggested starting from molecular dynamics results. In particular, it is found that the dissociation rate is only weakly dependent on the cluster total angular momentum J for the three cluster sizes considered. This would allow one to partially neglect the J-dependency of the kinetic coefficients, leading to a substantial decrease in the computational effort needed for the complete description of the cascade process. The impact of this investigation on the modeling of the nucleation process is discussed.

“…A Markov walk was used to generate a microcanonical distribution of initial atomic positions and velocities for the classical trajectories. 33 The number of Markov chain steps per trajectory and Markov step length were set at 500 and 0.15 Å, respectively, for all fragments. If a saddle point is used as the initial reference geometry, the Markov walk will wander downhill to products or reactants unless constrained to remain in the saddle point vicinity.…”

Section: Classical Trajectory Methodsmentioning

confidence: 99%

Growing multiconfigurational potential energy surfaces with applications to X+H2 (X=C,N,O) reactions

Netzloff

Collins

Gordon

2006

A previously developed method, based on a Shepard interpolation procedure to automatically construct a quantum mechanical potential energy surface (PES), is extended to the construction of multiple potential energy surfaces using multiconfigurational wave functions. These calculations are accomplished with the interface of the PES-building program, GROW, and the GAMESS suite of electronic structure programs. The efficient computation of multiconfigurational self-consistent field surfaces is illustrated with the C+H2, N+H2, and O+H2reactions. KeywordsSurface states, Hydrogen reactions, Interpolation, Potential energy surfaces, Exchange reactions Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Phsyics 124, 154104, and may be found at doi:10.1063/ 1.2185641. Growing multiconfigurational potential energy surfaces with applications to X + H 2 "X = C , N , O… reactions A previously developed method, based on a Shepard interpolation procedure to automatically construct a quantum mechanical potential energy surface ͑PES͒, is extended to the construction of multiple potential energy surfaces using multiconfigurational wave functions. These calculations are accomplished with the interface of the PES-building program, GROW, and the GAMESS suite of electronic structure programs. The efficient computation of multiconfigurational self-consistent field surfaces is illustrated with the C + H 2 , N+H 2 , and O + H 2 reactions.