TIP4P2005 water with kspace_style pppm/tip4p

Hi,

I am calculating the surface tension of TIP4P2005 water model. Is it that I have to use kspace_style pppm/tip4p or ewald or pppm can be used as well without error?

Please let me know.

Also can anyone tell me what is the best setting for Nevery-Nrepeat-Nfrequency so that I get a valid and closest to experimental value for surface tension of this model.

Thanks,

Neha Sinha

India

The tip4p style is required to ensure that the massless charge site is correctly handled. You'll get bad results using a non-tip4p kspace style with TIP4P/2005.

--AEI

Thanks Ahmed. I read that in manual too.

Should I include any information regarding the massless site charge in the datafile.
From lammps manual , my specifications in the data file is O charge = -1.1128
H charge = 0.5564

however, I have read in papers ( http://scitation.aip.org/content/aip/journal/jcp/132/1/10.1063/1.3279128 )that the oxygen atom carries no charge and the massless site does.

I am asking all this because my surface tension value coming out is low , by using tip4p kspace_style, when compared to the results in the paper I am referring to ( http://scitation.aip.org/content/aip/journal/jcp/126/15/10.1063/1.2715577 ) so

Sincerely,

Neha

Thanks Ahmed. I read that in manual too.

Should I include any information regarding the massless site charge in the datafile.
From lammps manual , my specifications in the data file is O charge = -1.1128
H charge = 0.5564

however, I have read in papers ( http://scitation.aip.org/content/aip/journal/jcp/132/1/10.1063/1.3279128 )that the oxygen atom carries no charge and the massless site does.

No, the code automatically calculates the position of the massless site, and assigns it the charge of the oxygen.

I am asking all this because my surface tension value coming out is low , by using tip4p kspace_style, when compared to the results in the paper I am referring to ( http://scitation.aip.org/content/aip/journal/jcp/126/15/10.1063/1.2715577 ) so

You may be neglecting the long-range correction to the surface tension that occurs when a cutoff is used. You have two options: use pppm/disp/tip4p, which includes the long-range behavior explicitly, or compute it as a post-processing step.

–AEI

When I am using kspace style pppm/disp/tip4p with pair style lj/cut/tip4p/long, I get error

"KSpace style is incompatible with Pair style"

I am running on lammps15May15 version.

When I am using * kspace style pppm/disp/tip4p* with pair style
*lj/cut/tip4p/long*, I get error

*"KSpace style is incompatible with Pair style*"

​as you should. pppm/disp/tip4p requires lj/long/tip4p/long

please re-read the documentation and read rolf's paper about how to do such
calculations correctly. if not, you will be wasting your time.

axel.​