Subject: 100% parallel algorithm in MD

From: [email-masked] (Noy)
Date: Thu, 27 Oct 1994 14:00:49 +0100 (NFT)

Dear cyberchemists,
        From the principle of molecular dynamics, velocity is
reversible. Thus, if we assign a minus sign to all velocity of every
particle in the simulation box ( at any equilibrated state ), the
trajectory should be recoverd to the past correctly. 
        This is not a new idea but I wonder if somebody has
practiced it. For example if we simulate the phase space at time
orgin t0 to the time t1,
        
        t0 ---------------->   t1     (1 picosecond)

        Then, we revert velocity of all particles of the configuration
at the time t0. Simulates it back to the past to the time t2

        t0 ---------------->   t2     (1 picosecond)

        Then we have the past trajectory.
        If we connect the two trajectories together, we will have

         t2 -------------------> t0 -----------------> t1 (2 picoseconds)
       
        Thus, we must revert the sign of velocity of the configurations
from the time t1 to the time t0. We will have the overall longer trajectory
of the simulation. Given the run of two trajectories running in parallel
on two computers, one can save time by the factor of 2. 
        The dynamics and structural properties should be calculated
from the time origin t2 to the time t1.
        Does somebody have comments or suggestions on this ? Is it
correct ? If this idea is practical, it would help to save time a lot.
Imagine if I have to run MD for 10 ps to evaluate diffusion coefficient
more precisely, I can divide the work into 2 jobs. One job is simulated
on a computer. For another job, I convert the velocity and trace the
phase space back to it past, have it run on another computer parallelly.
Connect two jobs together by going back to the origin of the phase space
in the far past time. Evaluate the time evolution and then I should
get the results much faster. After all, the parallel efficiency is 
100 %  !!!!!!!!
        Thanks for your comments.
                                                best wishes,
                                                Teerakiat