Re: [AMBER-Developers] thoughts on gamma_ln?

From: Ross Walker <ross.rosswalker.co.uk>
Date: Wed, 9 Mar 2016 08:56:54 -0700

> Didn't the code use to quit with an error telling you gamma_ln needed to be set if you set ntt=3 and didn't change it. Did this change at some point?

>From mdin_ctrl_dat.F90 in pmemd

  gamma_ln = 0.d0 !Default is zero but if ntt=3 we set it to 1.0d0

  if (gamma_ln .gt. 0.d0 .and. ntt .ne. 3) then
    write(mdout, '(a,a)') error_hdr, 'ntt must be 3 if gamma_ln > 0!'
    inerr = 1
  end if

  if ( ntt == 3 .and. ntb == 2) then
    !Require gamma_ln > 0.0d0 for ntt=3 and ntb=2 - strange things happen
    !if you run NPT with NTT=3 and gamma_ln = 0.
    if ( gamma_ln <= 0.0d0 ) then
      write(mdout,'(a,a)') error_hdr, 'gamma_ln must be > 0 for ntt=3 with ntb=2.'
      inerr = 1
    end if
  end if

So it requires it for NTP runs and the comment implies it is set to 1.0 for ntt=3 but never actually is. So close to what you want...


> On Mar 9, 2016, at 07:55, Carlos Simmerling <carlos.simmerling.gmail.com> wrote:
>
> Sorry that wasn't clear - I support changing it.
> On Mar 9, 2016 9:34 AM, "Carlos Simmerling" <carlos.simmerling.gmail.com>
> wrote:
>
>> I would agree, users could I tend to turn it on (ntt) but have it not
>> really turn on....
>> On Mar 9, 2016 9:33 AM, "Adrian Roitberg" <roitberg.ufl.edu> wrote:
>>
>>> Hi
>>>
>>> The default for gamma_ln for langevin thermostat (ntt=3) is =0, which
>>> basically means constant energy. Obviously, when you use shake and a
>>> dt=0.002 energy is not really conserved, so there is trouble.
>>>
>>> Should we keep it as 0 or change it to something small but useful, like 1?
>>>
>>> adrian
>>>
>>> --
>>> Dr. Adrian E. Roitberg
>>> Professor.
>>> Department of Chemistry
>>> University of Florida
>>> roitberg.ufl.edu
>>> 352-392-6972
>>>
>>>
>>> _______________________________________________
>>> AMBER-Developers mailing list
>>> AMBER-Developers.ambermd.org
>>> http://lists.ambermd.org/mailman/listinfo/amber-developers
>>>
>>
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