Subject: NPT ensemble and P fluctuations

From: "Gustavo A. Mercier Jr" <[email-masked]>
Date: Mon, 4 Nov 1996 07:54:19 -0500 (EST)

Hi!

I am running an NPT ensemble using the Berendsen method to
scale the Temperature and Pressure. In 25ps the temperature has
stabilized within 2-3deg from the 300K target. The energy is pretty
stable (although I know it should not be conserved). The dimensions
of the periodic box have also stabilized (although the box volume
is not meant to be conserved). The density is 
also stable at 0.98-0.99 (Solvent is water.) 

The solute is a generation 2 PAMAM dendrimer and it is in a box 
with 3500 water molecules.

I am using the module SANDER from AMBER 4.1 with all patches up
to bugfix.77.

**Problem**: The pressure is converging very slowly...
It fluctuates widely 80-100kbars with the average close to -1.0-+5.0kbars.

Right now the coupling constants are 0.1ps for both temp and pressure.

**Question**:Are there any tricks to speed up the equilibration of the 
pressure?

I will summarize to the net if there is interest.

Thanks for your kind reply!

-- 
                                      ("`-/")_.-'"``-._
Gustavo A. Mercier,Jr.,MD,PhD         (. . `) -._    )-;-,_() 
Division of Nuclear Medicine          (v_,)'  _  )`-.\  ``-
Dept. of Radiology                    _;- _,-_/ / ((,'
University of Pennsylvania           ((,.-'  ((,/
3400 Spruce St.                  [email-masked]
Philadelphia, PA 19104         215-662-3069/3091 fax: 215-349-5843