GROMACS version:2021.4

GROMACS modification: Yes/No

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Dear Gromacs users,

I would like to calculate enthalpy using gmx energy. I did not find in manual how enthalpy is culculated.

Please, could you explain me, how is enthalpy calculated using gmx energy command.

Hi

Sorry I am not sure I understand your question. Did you run gmx energy and get as output enthalpy ? If yes, which option did you use?

Or do you ask how to get the enthalpy of the system?

/Alessandra

Dear Alessandra,

I used gmx energy to calculate enthalpy using option 23, please see below

```
1 Bond 2 Angle 3 Proper-Dih. 4 LJ-14
5 Coulomb-14 6 LJ-(SR) 7 Disper.-corr. 8 Coulomb- (SR)
9 Coul.-recip. 10 Potential 11 Kinetic-En. 12 Total-En ergy
13 Temperature 14 Pres.-DC 15 Pressure 16 Constr.- rmsd
17 Box-X 18 Box-Y 19 Box-Z 20 Volume
21 Density 22 pV 23 Enthalpy 24 Vir-XX
25 Vir-XY 26 Vir-XZ 27 Vir-YX 28 Vir-YY
29 Vir-YZ 30 Vir-ZX 31 Vir-ZY 32 Vir-ZZ
33 Pres-XX 34 Pres-XY 35 Pres-XZ 36 Pres-YX
37 Pres-YY 38 Pres-YZ 39 Pres-ZX 40 Pres-ZY
41 Pres-ZZ 42 #Surf*SurfTen 43 Box-Vel-XX 44 Box-Vel- YY
45 Box-Vel-ZZ 46 T-System
```

However, I did not find in the Gromacs manual using what mathematical equation enthalpy is calculated. Could you please explain me, how this characteristic is calcualted?

Best regards,

Yel21.

Hi

I think it is calculated as E(tot) + pV . You can check if by printing 12, 22, 23.

\Alessandra