Calculation of Enthalpy

LAMMPS LAMMPS Beginners
1

I want to calculate enthalpy based on the paper referenced here.My potential is the same as the one used by the author, and I am using the LAMMPS code provided by the author. however, when I calculate the enthalpy difference for T=1000 and T=300 (i.e., h(1000)−h(300)), I do not obtain the same result as reported in the paper. (i subtract the average enthalpy by the number of atoms and then multiply the result by 96.49 to convert from eV to kJ/mol.)

here is my code:

# set periodic boundaries, units and thero-baro damping
boundary p p p
atom_style full
units metal
variable THERMO_DAMP equal 0.1
variable BARO_DAMP equal 0.5

# import UO2 single cell fluorite structure and assign atom labels
read_data UO2-single_cell.lmpstruct
variable O equal 1
variable U equal 2

# set charges
set type $O charge -1.1104
set type $U charge 2.2208

# define interatomic potential via coulombic and embed_UO2.fs tabulation 
kspace_style pppm 1.0e-5
variable SR_CUTOFF equal 11.0
pair_style hybrid/overlay coul/long ${SR_CUTOFF} eam/alloy
pair_coeff   *    *    coul/long
pair_coeff   *    *    eam/alloy CeThUNpPuAmCmO.eam.alloy O U

#Perform minimization
fix boxrelax_fix all box/relax aniso 0.0 vmax 0.001
thermo 1
thermo_style custom step cpu press etotal lx cella cellb cellc cellalpha cellbeta cellgamma
min_style sd
min_modify line quadratic dmax 0.05
minimize 1.0e-25 1.0e-25 1000 10000
unfix boxrelax_fix


# Create 4x4x4 supercell containing 768 atoms
replicate 4 4 4

# create initial velocities and set timestep
velocity all create 300 160278
timestep 0.002

# Set-up thermostat
fix thermostat_fix all npt temp 300 300 ${THERMO_DAMP} aniso 0.0 0.0 ${BARO_DAMP}

thermo_style one
thermo 10

neigh_modify delay 0 every 1 check yes

# equilibrate for 50ps
run 25000

Here is the enthalpy per step from my simulation.

Screenshot from 2024-11-09 14-18-06
Screenshot from 2024-11-09 14-18-061125×738 45.3 KB

2

So is there a question about LAMMPS here?

You simply state that you do not reproduce the results from the reference paper.

3

Apologies for not clearly stating my question earlier. the issue is that my enthalpy difference isn’t correct, and I want to reproduce the author’s results but i can’t.

4

You already stated that and that is not a question, let alone a question about LAMMPS.

5

Does my LAMMPS code produce the correct enthalpy?

6

That is not a LAMMPS question, but a question about your research.
Obviously, your input file is syntactically correct, or else it would not run.

How you choose settings, what model you use, whether you get the results you desire are things that you have to figure out for yourself. That is what makes this research!
That also makes this a topic for discussion with your adviser or tutor or - in case both of you cannot find a flaw in the input - a discussion with the authors of the publication that you want to reproduce.

Please also keep in mind that you are asking for a lot with your question. It is not that somebody would just look at your input and say “yes” or “no”. One would have to spend time studying the reference paper, setting up the same kind of simulation (successfully) and then compare that to your input. That is a lot of work and why would somebody do that for you (out of kindness and without having any benefits)?