Empirical potential energy surfaces relating structure and activation energy. 1. Metallacyclopentene ring inversion in (s-cis-.eta.4-butadiene)metallocene complexes and related compounds

1988 ◽  
Vol 110 (15) ◽  
pp. 4953-4957 ◽  
Author(s):  
Hans Beat. Buergi ◽  
Katharina C. Dubler-Steudle
Keyword(s):  
Activation Energy ◽  
Potential Energy ◽  
Potential Energy Surfaces ◽  
Ring Inversion ◽  
Empirical Potential ◽  
Energy Surfaces ◽  
Related Compounds ◽  
Metallocene Complexes

Empirical Potential-Energy Surfaces Fitting Using Feed forward Neural Networks

2012 ◽  
Author(s):  
Lionel Raff ◽  
Ranga Komanduri ◽  
Martin Hagan ◽  
Satish Bukkapatnam
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Potential Energy Surfaces ◽  
Force Fields ◽  
Pair Potential ◽  
Potential Surfaces ◽  
Empirical Potential ◽  
Functional Forms ◽  
Dynamics Simulations ◽  
Energy Surfaces

When the system of interest becomes too complex to permit the use of ab initio methods to obtain the system potential-energy surfaces (PES), empirical potential surfaces are frequently employed to represent the force fields present in the system under investigation. In most cases, the functional forms present in these potentials are selected on the basis of chemical and physical intuitions. The parameters of the surface are frequently adjusted to fit a very small set of experimental data that comprise bond energies, equilibrium bond distances and angles, fundamental vibrational frequencies, and perhaps measured barrier heights to reactions of interest. Such potentials generally yield only qualitative or semiquantitative descriptions of the system dynamics. Several research groups have significantly improved the accuracy of the values of the experimental properties computed using empirical potential surfaces by fitting the chosen functional form for the potential to the force fields obtained from trajectories using ab initio Car-Parrinello molecular dynamics simulations. The fitting to the force fields is usually done using a least-squares fitting approach. This method has been employed by Izvekov et al. to obtain effective non-polarizable three-site force fields for liquid water. Carré et al. have employed such a procedure to obtain a new pair potential for silica. In their investigation, the vector of potential parameters was fitted using an iterative Levenberg-Marquardt algorithm. Tangney and Scandolo have also developed an interatomic force field for liquid SiO2 in which the parameters were fitted to the forces, stresses, and energies obtained from ab initio calculations. Ercolessi and Adams have used a quasi-Newtonian procedure to fit an empirical potential for aluminum to data obtained from first-principals computations. Empirical potentials can be improved by making the parameters parameterized functions of the coordinates defining the instantaneous positions of the atoms of the system. This approach has been successfully employed by numerous investigators The difficulty with this procedure is that the number of parameters that must be adjusted increases rapidly. Appropriate fitting of these parameters requires a much more extensive database. Finally, the actual fitting process can often be tedious, difficult, and time-consuming.

scholarly journals Dynamics of chemical reactions of astrophysical interest

1997 ◽  
Vol 178 ◽  
pp. 271-280 ◽  
Author(s):  
M. Alagia ◽  
N. Balucani ◽  
L. Cartechini ◽  
P. Casavecchia ◽  
G.G. Volpi
Keyword(s):  
Potential Energy ◽  
Ab Initio ◽  
Chemical Reactions ◽  
Potential Energy Surfaces ◽  
Experimental Results ◽  
Empirical Potential ◽  
Beam Scattering ◽  
Scattering Technique ◽  
Energy Surfaces ◽  
Semi Empirical

The dynamics of the astrophysically relevant reactions OH + H2,OH+CO,N(2D)+C2H2 and O(1D)+H2 are studied using the crossed beam scattering technique. Comparisons of the experimental results with those of dynamics calculations on ab initio and semi-empirical potential energy surfaces are discussed.

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