Force field methods energy types

A quantitative measure of thermal stability is the lattice energy of the compound. This may be evaluated by the method of atom-atom potentials using the refined atomic positions derived from accurate crystal structure determinations. One may employ force fields of the type ... 

Force-field methods form the basis of molecular dynamics. They use a parameterised quasi-classical description of interatomic forces to model the trajectory of systems typically composed of hundreds or even thousands of atoms. One good feature of these types of calculations is that with large systems the computational effort increases linearly with the size of the problem. This means that increased computational power allows considerably larger systems to be studied. Further gains can also be made by using parallel processors since energy calculations in molecular dynamics simulations are inherently parallel. 

CHARMM The Energy Function and Its Parameterization Continuum Solvation Force Fields A General Discussion Molecular Surface and Volume OPLS Force Fields Poisson-Boltzmann Type Equations Numerical Methods Proton Affinities. 

Direct dynamics calculations of the type just described, with all degrees of freedom included, are very expensive if the local quadratic approximations to the potential energy surface are obtained from an ab initio computation. In applications we have used a hybrid parameterized quantum-mechanical/force-field method, designed to simulate the CASSCF potential for ground and covalent excited states. A force field is used to describe the inert molecular a-framework, and a parameterized Heisenberg Hamiltonian is used to represent the CASSCF active orbitals in a valence bond space. Applications include azulene and benzene excited state decay dynamics. 

Free Energy Calculations Methods and Applications Free Energy Perturbation Calculations Free Energy Simulations Hydrogen Bonding 1 Hydrogen Bonding 2 Molecular Dynamics DNA Molecular Dynamics Simulations of Nucleic Acids Molecular Dynamics Techniques and Applications to Proteins Nucleic Acid Force Fields Poisson-Boltzmann Type Equations Numerical Methods Protein Force Fields. 

While simulations reach into larger time spans, the inaccuracies of force fields become more apparent on the one hand properties based on free energies, which were never used for parametrization, are computed more accurately and discrepancies show up on the other hand longer simulations, particularly of proteins, show more subtle discrepancies that only appear after nanoseconds. Thus force fields are under constant revision as far as their parameters are concerned, and this process will continue. Unfortunately the form of the potentials is hardly considered and the refinement leads to an increasing number of distinct atom types with a proliferating number of parameters and a severe detoriation of transferability. The increased use of quantum mechanics to derive potentials will not really improve this situation ab initio quantum mechanics is not reliable enough on the level of kT, and on-the-fly use of quantum methods to derive forces, as in the Car-Parrinello method, is not likely to be applicable to very large systems in the foreseeable future. 

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