Re: [gmx-users] Maximum Force constant for Position Restraints

2015-04-22 Thread David van der Spoel
On 2015-04-21 21:40, Alex wrote: No, it does not depend on the system content, aside from the mass of the particle. For a simulation requiring numerical integration in time, there is a limit, and I just estimated it above. For the real world, the limit is that there's no such thing as a harmonic

Re: [gmx-users] Maximum Force constant for Position Restraints

2015-04-22 Thread Alex
David, that's exactly right. For every timestep value, one can derive the appropriate upper limit for the restraint constant in a somewhat physically sound manner. I am just not entirely sure what was the purpose of the initial question, because for infinite restraint constant, I'd just freeze

Re: [gmx-users] Maximum Force constant for Position Restraints

2015-04-21 Thread Alex
No, it does not depend on the system content, aside from the mass of the particle. For a simulation requiring numerical integration in time, there is a limit, and I just estimated it above. For the real world, the limit is that there's no such thing as a harmonic position restraint. :) If you want

Re: [gmx-users] Maximum Force constant for Position Restraints

2015-04-21 Thread Alex
I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau = sqrt(m/k), where m is the mass of the lightest restrained particle in the system, k is the constant you seek, and tau is the timestep. The coefficient is four because of the

Re: [gmx-users] Maximum Force constant for Position Restraints

2015-04-21 Thread Alex
Correction: tau/pi on the left for the highest value and 5*tau/pi for the 10 x period suggestion above. On Tue, Apr 21, 2015 at 1:13 PM, Alex nedoma...@gmail.com wrote: I think this can be estimated from a general physical argument. The absolute max in my opinion should come from 4*pi*tau =

Re: [gmx-users] Maximum Force constant for Position Restraints

2015-04-21 Thread Marcelo DepĆ³lo
Thanks Alex. But then, theoretically, is there no limit? All depends on your system's content, right? 2015-04-21 16:16 GMT-03:00 Alex nedoma...@gmail.com: Correction: tau/pi on the left for the highest value and 5*tau/pi for the 10 x period suggestion above. On Tue, Apr 21, 2015 at 1:13 PM,