[gmx-users] What is wrong with enthalpy?

[Igor Shchechkin]

>On 2015-02-10 18:58, Igor Shchechkin wrote:
>> Dear Gromacs users,
>>
>>I have changed from 4.5.3 to 4.6.5 version and then continued
>> simulation of Protein+Ligands+water+ions system, having used new
>> created .tpr file and .cpt file produced by the latter run of 4.5.3
>> version. All went normally, but when I evaluated enthalpy, it appeared
>> to jump from -1.16e6 to -0.67e6.
>> (Earlier I encountered such phenomenon when changed from 4.5.3 to 4.5.5)
>> What is the cause of this?
>>
>> Best regards,
>> Igor Shchechkin
>>

>How did you extract it?

I entered command:
g_energy -f Jwi-73.edr -o Jwi-73.VH.xvg
then got "number-value" table, then typed numbers corresponding to
Volume (21) and Enthalpy (24).
(Volume has jump too, but slight one, unlike enthalpy)

>Enthalpy = Total Energy + pV
>I think the main change was to store the Enthalpy directly in the energy
>file at some point.
>Please try to check whether the total energy is the same.

I chechked total energy; really Enthalpy appears to be equal to Total
Energy + pV.

>In general it is not recommended to change software version during a
>project.

>--
>David van der Spoel, Ph.D., Professor of Biology
>Dept. of Cell & Molec. Biol., Uppsala University.
>Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205.
>spoel at xray.bmc.uu.se    http://folding.bmc.uu.se

Igor Shchechkin