Introduction to Enhanced Sampling Strategies

When calculating free energies, one generates, either by molecular dynamics or MC, configuration space samples distributed according to a probability distribution function (e.g., the Boltzmann distribution in the case of the Helmholtz free energy). 

We start by reminding the reader of the original and seminal ideas of Torrie and Valleau, introduced in Chap. 3. In doing so, we thereby prepare for the subsequent sections in this chapter. 

To handle broken ergodicity in the calculation of thermodynamic averages (i.e., time-independent averages of the type (A) oc / /I (x) exp(— ft77(x))dx) a host of methods have been devised [2]. In a subset of these, the Boltzmann distribution is altered and replaced with a more delocalized one, w(E). One is thus able to generate (faster) samples distributed according to w and subsequently, one can use importance 

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