# [gmx-users] Calculate heat capacity

Ilya Chorny ichorny at maxwell.compbio.ucsf.edu
Wed Mar 17 07:37:00 CET 2004

```I'm not sure what gromacs does to calc Cv. I get a different reult as well.

Ilya

-----Original Message-----
Behalf Of Jia-Lin Lo
Sent: Tuesday, March 16, 2004 9:53 PM
To: gmx-users at gromacs.org
Subject: Re: [gmx-users] Calculate heat capacity

Hi,
I use your algorithm to test.  The value is much different from
g_energy's result.
g_energy : ~ 10( J/mole * K)
I take a look  about gmx  source code. There is one paraghaph about
heat capacity.

VarT = RMSD(T) * RMSD(T),  kb = 8.31451
factor = nmol*ndf*VarT/(3.0*Temp*Temp)
nmol = 1, ndf = 3
Cv = kb / (2/3 - factor)

It seems has no relationship with energy.  I am confused.

Jia-lin

----- Original Message -----
From: Ilya Chorny
To: gmx-users at gromacs.org
Sent: Wednesday, March 17, 2004 12:00 PM
Subject: RE: [gmx-users] Calculate heat capacity

The heat capacity is proportional to the second moment (variance) of the
energy.
<sigma(E)^2> = k*T^2*Cv

Ilya

-----Original Message-----
[mailto:gmx-users-admin at gromacs.org]On Behalf Of Jia-Lin Lo
Sent: Tuesday, March 16, 2004 6:59 PM
To: gmx-users at gromacs.org
Subject: [gmx-users] Calculate heat capacity

Hi,
I am doing a simple simulation ( protein in water). When I use
g_energy to monitor the  energy change, there are several statistical
values
printed on screen. I notice the last line is the heat capacity value.
I would
like to know how does it to be calculated?  Is there any formula for
it ?
I want to write a program to calculate it by myself.