Here are the most famous and efficient barostats for NPT simulations:

Anderson barostat:

H. C. Andersen. J. Chem. Phys., 72:2384 (1980)

In this case you allow only the cell dimensions to vary isotropically under average constant pressure.

The modified version of the Anderson barostat by Parinallo and Rahman where shape and volume could change at the same time:

M. Parrinello and A. Rahman. Phys. Rev. Lett., 45:1196–1199 (1980).

M. Parrinello and A. Rahman. J. Chem. Phys., 76:2662 (1982).

M. Parrinello and A. Rahman. J. Chem. Phys., 80:860 (1984).

M. Parrinello and A. Rahman. J. Appl. Phys., 52:7182 (1981)

Both are implemented in CPMD and CP2K.

More general and detailed description could be found here:

http://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDAQFjAB&url=http%3A%2F%2Famutiara.staff.gunadarma.ac.id%2FDownloads%2Ffiles%2F5979%2Fmarx.pdf&ei=bwLBVJeNCsmyUeD6g5gB&usg=AFQjCNE07AW2xQFy3NuxXY0nNvDgg2VFWw&sig2=1civ2lHXzJ8J3j3suecCAA

Best,

Assil

in MDS, we can choose either set up NVT or NPT. if we choose to constant the NVT, thus we can specific the pressure

Simplest method is to update the size of the simulation box (if you decrease the box volume, pressure will increase, and vice versa)

edit:

In GROMACS:

http://manual.gromacs.org/current/online/mdp_opt.html#pc

Looking at NAMD or GROMACS manual, for example, is very well explained (and easy top use)  how to set up thermostat and/or barostats to simulate your system as NVE or NPT

all friends

thanks for your help. but i need the description of the algorithm. i found that in computer simulation pressure has been set with Clausius theorem. could you pleas explain it for me?

You can find information about the Clausius theorem and the virial theorem in their respective wikipedia pages. You might also find the following lecture on MD simulations useful (it includes a sub chapter on pressure):

http://dasher.wustl.edu/bio5476/lectures/lecture-06.pdf

However, it would be easier if you just told us what MD suite you have been using and which pressure control method you have employed, so that we could direct you to more specific sources on the algorithms.

In any case, one of the most widely used pressure control methods, particularly for GROMACS users, is the Berendsen barostat. You can find the original paper describing their pressure coupling control method in this link:

http://scitation.aip.org/content/aip/journal/jcp/81/8/10.1063/1.448118

Most NAMD users, on the other hand (myself included), usually work with Langevin dynamics for temperature and combine it with the Langevin piston method, which is essentially an adaptation of the Nose-Hoover algorithm (originally designed for temperature) to pressure control. The paper of the method is in the following link:

http://physics.ujep.cz/~mlisal/md/martyna-tobias-klein_md.pdf

Both papers describe  their respective algorithms in extensive detail so, if you have been using any of these, they will probably prove useful.

Hope I helped.

Here are the most famous and efficient barostats for NPT simulations:

Anderson barostat:

H. C. Andersen. J. Chem. Phys., 72:2384 (1980)

In this case you allow only the cell dimensions to vary isotropically under average constant pressure.

The modified version of the Anderson barostat by Parinallo and Rahman where shape and volume could change at the same time:

M. Parrinello and A. Rahman. Phys. Rev. Lett., 45:1196–1199 (1980).

M. Parrinello and A. Rahman. J. Chem. Phys., 76:2662 (1982).

M. Parrinello and A. Rahman. J. Chem. Phys., 80:860 (1984).

M. Parrinello and A. Rahman. J. Appl. Phys., 52:7182 (1981)

Both are implemented in CPMD and CP2K.

More general and detailed description could be found here:

http://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDAQFjAB&url=http%3A%2F%2Famutiara.staff.gunadarma.ac.id%2FDownloads%2Ffiles%2F5979%2Fmarx.pdf&ei=bwLBVJeNCsmyUeD6g5gB&usg=AFQjCNE07AW2xQFy3NuxXY0nNvDgg2VFWw&sig2=1civ2lHXzJ8J3j3suecCAA

Best,

Assil

dear all

thanks for your useful suggestions.