ComPhy/Sorkin Viacheslav<

It is well known, that energy landscape of many important physics system like spin glasses or
biological macromolecules is characterized by a multiple local minima separated by high energy barriers.

The conventional methods like Molecular Dynamics or
Simulated Annealing will sometimes get trapped in the configurations corresponding to one of these
local minima.
Hence, only small part of the entire space are explored in finite time of computer simulation
and physical quantities cannot be investigated accurately .

One effective way to overcome this difficulty is to perform a simulation in so called
generalized ensemble
, where the probability to cross an energy barrier is independent of temperature.

The
simulated tempering
is one of prominent example of the generalized ensemble technique.

The
simulated tempering
was originally introduced as a method for calculation of a free energy
in a model of electrolite A.P.Lyubartsev et al., J.Chem.Phys. 96 1776 (1992) and as an algorithm for overcoming a multipleminima problem in a random field Ising model
E.Marinari and G.Parisi, Europhys. Lett. 69 2292 (1992).

In general, in this method
the series of Monte Carlo steps with the local updates at definite temperature T are performed and
than the temperature is changed
according to Metropolis algorithm. In another worlds, the random walk in the discrete one dimensional temperature space
is carried out (See the picture). The most difficult problem in this approach is to determine probabilties
for transitions between
various states with different temperature.

The main idea of the project is to apply the simulated tempering method
in order to investigate point defects, namely vacancies and
interstitials , in metals with bcc structure (Vanadium)
as well as with fcc structure (Copper). For this purpose the EAM (Vanadium )and TB (Copper) potentials are exploited.
The off lattice MC simulation is implemented. The probabilties for transition between
various states with different temperature will be calculated by means the simplest approach proposed in the first
articles devoted to the problem.

The program is written in C language and visualization and animatione is performed by means
the interactive Aviz package .
54 Atoms .
Point Defects:Interstitial 128+1 Atoms .
Point Defects:Interstitial 128+1 Atoms Top View.
Point Defects:Interstitial 128+1 Atoms.
The Interstial Motion .
The Potential Energy .
The Histogram .
This the example of an interstitial placed between the Vanadium atoms.
You can download the program
Simulated Tempering which is a program that simulates Vanadium
(See the readme.file )
Please direct questions or comments to Sorkin V.A.
Last updated May 22, 2001
Computer Physics:The Home Assignments
My Projects: Simulated Tempering
Software  MD & MC Simulations  Laboratory 2 MP