dielectric constant of water

[jess_white]

Hi,

I was wondering if there is a way to add in the INCAR the dielectric constant of water? Such as to make it 73 (room temperature) and 20 (higher temperature)? I would love to add that my calculation so its not just a static calculation and makes better comparison

I tried to google it and I can only find: wiki/index.php/Dielectric_properties_of_SiC
Which I don't think is what I am looking for as I want to be able to change the constant and not just turn it on.

Cheers,
Jess

[jonathan_lahnsteiner2]

Dear Jess White,

It is possible to set a dielectric constant in the VASP INCAR file. Please check the related VASP wiki page of EPSILON.
I hope this is what you are looking for.

All the best Jonathan

[jess_white]

Thanks so much Jonathan! So I just change the epsilon in the INCAR? Also this is just a silly question --> so for the dielectric I don't have to specify its water do I as each chemical has a different EPSILON? So if I put 73 it assumes water? Also do I need to add anything else into the INCAR? Or keep it the same and just add that tag and do the normal DFT?

[jonathan_lahnsteiner2]

Dear Jess White,

You don't have to change anything in your INCAR file. It is sufficient to add the line

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EPSILON = 73

into your INCAR file. You don't have to specify what kind of dielectric is included. The numerical value of the EPSILON tag will already specify which dielectric it is.
VASP will use the value which you supply with the EPSILON tag and scale electrostatic interactions by it.

All the best Jonathan

[jess_white]

Thanks Jonathan So I did some calculations today and the energies were the same without the use of EPSILON. I am looking at the energies from OSZICAR. Does this mean that something is wrong or is this too be expected?

I am looking at a surface system and surface adsorption systems.

Many thanks,
Jess

[jess_white]

Here are the files which I submitted

[jonathan_lahnsteiner2]

Dear Jess White,

I was checking your calculation. The reason you don't see any difference in energies by setting EPSILON is because as mentioned on the wiki page it will scale the monopole and dipole interactions in your system. Since your system is not charged there will be no monopole interactions. The dipole moment of your system is very small

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 dipolmoment           0.000000      0.000000      0.028701 electrons x Angstroem

and therefore the energy will not change when scaling these dipole interactions by the input epsilon EPSILON.
You can check the dipole moment of your box in the OUTCAR file with the following command.

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grep dipolmoment OUTCAR

Maybe you have to choose a more advanced way to include the effects of water in your system. You could do this by explicitly including water molecules into your simulation box. The temperature effect can then be modeled with molecular dynamics simulations. This will be computationally more costly but will give more realistic insight into your system.

All the best Jonathan