Ammm:Adaptive umbrella sampling

Multicanonical ensemble

Background of adaptive umbrella sampling

• Review of umbrella sampling (more details please refer to Yue's page)

    http://water.bme.utexas.edu/wiki/index.php/ABS:Umbrella_sampling_and_WHAM

    Umbrella sampling attempts to overcome the sampling problem by modifying the Hamiltonian so that

    the unfavorable states are sampled sufficiently. The modification can be written as a perturbation.

• The trial and error method for umbrella sampling

Theory of adaptive umbrella sampling

• Definitions

• The outline of the algorithm:

The potential energy as the variable for adaptive umbrella sampling

  The potential energy, in contrast to the commonly used umbrella potentials,

  is of particular interest for complex systems because it does not depend on

  assumptions about the geometry nor on a knowledge of the important

  conformations and transition states that are involved in the equilibration.

• Range of Sampling:

• Extrapolation of the Umbrella Potential:

Application:Threonine Dipeptide

• System setup
  • adaptive umbrella sampling runs were performed at 303 K.
  • T-min was set equal to 280 K, while T-max was set equal to 2000 K.
  • V-min ~ V-max set as -50 to 100 kcal/mol.
  • 200 bins.
  • The umbrella potential was represented as a linear combination of 40 trigonometric functions

• Results