[gmx-users] Free energy calculations with BAR and TI

[Tom Kirchner]

Hi Fernandez,

Actually, this is a known problem. You should find the description and 
solution in the archive. I had the same problem, so this may make your 
search more easy :)

The problem is in the code, at some point float and numbers are messed 
up, or something in this direction.

You can either edit the code and recompile gromacs or you substitute the 
temperatures with SED to a temperature nearly the same, 298 for example.

Ah, here is the link: 
http://gromacs.5086.n6.nabble.com/problem-with-g-bar-td4633215.html

Best
Tom Kirchner

On 11/02/2012 10:46 AM, Ignacio Fernández Galván wrote:
> Hi all,
>
> Can I use the same simulations (with delta_lambda=0, init_lambda and foreign_lambda) for TI and BAR calculations? I guess that boils down to whether the simulations with foreign_lambda are in equilibrium with the init_lambda, or they are some sort of hybrid ensemble between the different lambdas.
>
> Whatever the answer, I have another problem. I tried a BAR calculation and got this message with g_bar:
>
> Fatal error:
> Temperature in file 0.1.xvg different from earlier files or setting
>
> But the temperatures are all the same:
>
> $ grep 'T =' ?.?.xvg
> 0.0.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0"
> 0.1.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.1"
> 0.2.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.2"
> 0.3.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.3"
> 0.4.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.4"
> 0.5.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.5"
> 0.6.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.6"
> 0.7.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.7"
> 0.8.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.8"
> 0.9.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 0.9"
> 1.0.xvg:@ subtitle "T = 298.15 (K), \xl\f{} = 1"
>
> Is this maybe due to some numerical rounding error?
>
> Thanks
> Ignacio