[gmx-users] Velocity Verlet integrator

[Mario Fernández Pendás]

Dear all,

I am still interested in some integrator related issues.

I understand that the easiest way to implement velocity Verlet was to split
the updates in two updates. But I don't understad the order of those
updates.
I mean why there are two updates for velocities and then the update for
positions?
My intuitive idea would be to update first one half for velocities, then a
full step for positions and, finally, using these new positions the second
half for velocities.
Maybe I am missunderstanding something.

Thank you very much,
Mario Fernández-Pendás

2014-03-23 14:33 GMT+01:00 Michael Shirts <mrshirts at gmail.com>:

> Putting both velocity Verlet and leapfrog Verlet both in Gromacs turns
> out to be non-trivial for the bookkeeping.  The easiest way to do this
> was split the velocity Verlet updates.
>
> Also, the additional computational cost of two half steps for
> velocities is trivial compared to the cost of the forces for almost
> all systems.
>
> On Sun, Mar 23, 2014 at 8:39 AM, Mario Fernández Pendás
> <mariofp77 at gmail.com> wrote:
> > Dear all,
> >
> > In terms of computational efficiency, why the velocity Verlet integrator
> is
> > implemented in GROMACS in one full step for positions and two half steps
> > for velocities?
> >
> > Would it be more efficient to merge the second halft step for velocities
> > with the first half step of the following scheme, ie, integrating in one
> > full step for velocities?
> >
> > Thank you very much,
> > Mario Fernánez-Pendás
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