Good morning every body

Being a beginner, i wonder if it is any way to get the desired density,pressure by Lammps.

for example with copper at room pressure and temperature the density is 8.96 g/cm3.

Working in NVT if i adjust my system to get the appropriate density i lose the pressure and vice versa.

Best Regards

Good morning every body

Being a beginner, i wonder if it is any way to get the desired

density,pressure by Lammps.

for example with copper at room pressure and temperature the density is

8.96 g/cm3.

Working in NVT if i adjust my system to get the appropriate density i lose

the pressure and vice versa.

please note that this question has no relation to LAMMPS at all. you would

get the same behavior with any other MD software using the same settings

and parameters.

thus please go and have a discussion with your adviser about

parameterization for classical MD and how well (or not) potentials

represent experimental properties. it is worth reading the paper(s)

discussing the parameter set(s) you are using as well.

axel.

Thank you for your prompt answer, thankful for your all useful suggestions that help us to improve our scientific levels.

First we get a good results using Matlab program of classical molecular dynamics calculations many characteristics of copper (so we are mastering the use of all the parameters about this matter). We would like to make a system more complex so is very hard to achieve it by matlab.

So to get the desired density/pressure by Lammps in NVT we couldn’t.

for example with copper at room T= 300 K the density is 8.96 g/cm3.

to adjust it

Weight = (Number of atoms)*( atomic weight) = 2048*63,546= 130 142 g/mol

Volume = (Lattice fcc*Region block)^3= (28,906)^3= 24 152 a^3

Weight/Volume=5,38 g/(mol.a^3)=8,95 g/Cm^3

The pairwise potential used is Lennard-Jones : The same is used with matlab program gives a good results.

Depth of the potential well : 39.52

Finite distance: 2.3377

Rcut: 6.99

Normally in NVT group if i adjust my system to get the appropriate density i lose the pressure which should be approximately 1 atm.

Thank you for your prompt answer, thankful for your all useful suggestions

that help us to improve our scientific levels.

First we get a good results using Matlab program of classical molecular

dynamics calculations many characteristics of copper (so we are mastering

the use of all the parameters about this matter). We would like to make a

system more complex so is very hard to achieve it by matlab.

So to get the desired density/pressure by Lammps in NVT we couldn't.

for example with copper at room T= 300 K the density is 8.96 g/cm3.

to adjust it

Weight = (Number of atoms)*( atomic weight) = 2048*63,546= 130 142 g/mol

Volume = (Lattice fcc*Region block)^3= (28,906)^3= 24 152 a^3

Weight/Volume=5,38 g/(mol.a^3)=8,95 g/Cm^3

The pairwise potential used is Lennard-Jones : The same is used with matlab

program gives a good results.

Depth of the potential well : 39.52

Finite distance: 2.3377

Rcut: 6.99

so is what you are saying, that LAMMPS with the lj/cut potential is

wrong and your matlab code is correct?

do you have any other proof for that claim outside that your matlab

implementation matches your expectations in this specific case?

Normally in NVT group if i adjust my system to get the appropriate density i

lose the pressure which should be approximately 1 atm.

so what pressure *do* do get?

axel.