dipole moment of optimized water

[Rajendra Maharjan]

Greetings,

I did geometric optimization of water molecule to find out its dipole moment. However, on changing the cell size under 'ABC' and also the water configuration, I am constantly getting different dipole moment. Does the dipole moment of optimized water depend on cell size and water configuration? I think the dipole moment should be the same regardless of cell size and water configuration after geometry optimization.

Note: I used Barry phase formula for calculating dipole moment with 'PERIODIC=T'

Thank You

[Jürg Hutter]

Hi

two possibilities:
1) if you are doing periodic calculations, you have dipole-dipole interactions that
are cell dependent and lead to a very slow convergence of the local dipole.
2) If you check the cell dipole in the output file, you get polarization/cell volume.

regards
JH

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From: cp...@googlegroups.com <cp...@googlegroups.com> on behalf of Rajendra Maharjan <ryandra...@gmail.com>
Sent: Monday, November 14, 2022 1:00 AM
To: cp2k
Subject: [CP2K:18018] dipole moment of optimized water

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[Rajendra Maharjan]

Dear Professor,

I did geometry optimization of only a single water molecule to find its gas phase dipole moment using PBE/GTH-TZV2P method/basis set. I also did gas phase geometry optimization by turning off the cell pbc, but still I calculate different dipole moment of water. I also distorted the water molecule structure and the final optimized structure is fine with O-H covalent bond length of 0.97Å and 103.9° HOH bond angle. However, the dipole moment keep on changing if we change the cell size and also the water configuration.

I need the exact gas phase dipole moment of water using PBE/GTH-TZV2P for calculating its dipole moment in condensed phase.

Could you please help me how can I get accurate gas phase dipole moment of optimized water?

Thank You very much Professor for you reply.

Please find attached my input file to find out optimized water dipole moment.

Sincerely,

Rajendra Maharjan

[Rajendra Maharjan]

Making the box size very large (whether periodic cell or non-periodic), converges the dipole moment of water that is ~1.957 D using PBE/TZV2P-GTH method/basis set. Also, I did just single point calculation on the optimized water, that also match ~1.96 D water dipole moment.

Is this fine doing these methods to find gas phase water dipole moment?

Thank You very much.

Sincerely,

Rajendra Maharjan

[Jürg Hutter]

Hi
have a look at https://cccbdb.nist.gov/
to see the basis set dependence of the H2O dipole moment for many methods and
functionals.

regards
JH

________________________________________
From: cp...@googlegroups.com <cp...@googlegroups.com> on behalf of Rajendra Maharjan <ryandra...@gmail.com>

Sent: Monday, November 14, 2022 8:11 PM
To: cp2k
Subject: Re: [CP2K:18026] dipole moment of optimized water

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[Rajendra Maharjan]

Dear Professor,

Thank you! I will try to compare the gas phase dipole moment with NIST database.