# Heat capacity is NaN

**URL:** <https://gromacs.bioexcel.eu/t/heat-capacity-is-nan/12726>\
**Category:** User discussions\
**Created:** [October 2, 2025, 10:53am UTC](https://gromacs.bioexcel.eu/t/heat-capacity-is-nan/12726 "2025-10-02T10:53:13Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![sch](https://avatars.discourse-cdn.com/v4/letter/s/d26b3c/32.png) [@sch](https://gromacs.bioexcel.eu/u/sch)\
**Post date:** [October 2, 2025, 10:53am UTC](https://gromacs.bioexcel.eu/t/heat-capacity-is-nan/12726/1 "2025-10-02T10:53:13Z")

</div>

GROMACS version: 2024.3-plumed\_2.10.0  
GROMACS modification: No

Hi everyone,

I am trying to compute the heat capacity of TIP4P water with gmx dos. I’ve performed EM, 2 ns NVT equilibration with the Nosé-Hoover thermostat, 2 ns NPT equilibration with the Berendsen barostat, and another NPT run with the Parrinello-Rahman barostat once the system was equilibrated. My simulation box contains 2211 water molecules. To compute the heat capacity, I ran a 200 ps simulation with these parameters:

_; Run control  
integrator = md  
tinit = 0  
dt = 0.001  
nsteps = 200000 ; 200 ps  
nstcomm = 100_

_; Output control  
nstxout = 1  
nstvout = 1  
nstfout = 0  
nstlog = 20000  
nstenergy = 200  
nstxout-compressed = 10000_

Then I ran the command gmx dos -f prod\_Cp.trr -s prod\_Cp.tpr -dos dos.xvg -g dos.log. However, in the log file, I get:

_DoS parameters  
Delta = 0.179286  
fluidicity = 0.25113  
hard sphere packing fraction = 1.65778  
hard sphere compressibility = -2.98674  
ideal gas entropy = 0.0297878  
hard sphere entropy = 0.0187333  
sigma\_HS = 0.288443 nm  
DoS0 = 692.426  
Dos2 = 6.40987e+14  
DoSTot = 26513.1  
Diffusion coefficient from VACF 3.45092 10^-5 cm^2/s  
Diffusion coefficient from DoS 3.59111 10^-5 cm^2/s  
Heat capacity -nan J/mol K_

Any ideas why the heat capacity is NaN? Thanks!