Path integral free-energy perturbation and

The Integrated Path-Integral Free-Energy Perturbation and Umbrella-Sampling (PI-FEP/UM) Method... 

Major DT, Gao J (2007) An integrated path integral and free-energy perturbation-umbrella sampling method for computing kinetic isotope effects of chemical reactions in solution and in enzymes. J Chem Theory Comput 3 949—960... 

The centroid path integral method described above enable us to conveniently determine KIEs by directly computing the ratio of the quantum partition functions for two different isotopes through free energy perturbation (FEP) theory. The use of mass perturbation in free-particle bisection sampling scheme results in a major improvement in computation accuracy for KIE calculations such that secondary kinetic isotope effects and heavy atom isotope effects can be reliably obtained. The PI-FEP/UM method is the only practical approach to yield computed secondary KIEs sufficiently accurate to be compared with experiments. ... 

We have obtained a broad range of detailed quantitative results relating to universality in the absence of the electron-phonon interaction by various theoretical techniques. The methods include perturbation theory, the coherent potential approximation (CPA), field theory, path integral methods, numerical calculations and the potential well analogy. The results include the density of states, the nature of the wave functions, the mean free path, the energy dependent... 

Molecular dynamics and minimization of proteins locally enhanced sampling and free energy calculations along reaction paths by perturbation or thermodynamic integration. Stardent, Silicon Graphics, IBM, and HP workstations, moil-view for visualization of shaded spheres and sticks on Silicon Graphics. Available by anonymous ftp from 128.248.186.70. 

In thermodynamic integrations and multiple-step thermodynamic perturbations it is necessary to define a path that connects the initial and final states. This is done by formulating a A-dependent Hamiltonian such that 3. = 0 and k = 1 define the initial and final states, respectively. If only the free energy difference is needed, any path can be taken since the free energy is a thermodynamic state function. In practice, however, calculated systematic and statistical errors will depend on the particular path chosen. 

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