free energy calculation in pimd

[Webb Foo]

Hello everyone,

Can you explain me how to estimate the free energy profile from a pimd simulation, like constrained MD?

[Thomas Kühne]

Dear Webb Foo, 

using constrained MD the free energy profile can be computed in terms of the potential of mean force by means of the ensemble 

average of the Lagrange multipliers to constrain your reaction coordinate. You will find a particular good description in the SI of

the following paper: https://www.pnas.org/content/104/8/2626.short

However, when using PIMD, in my opinion the constraint has to be enforced on the ring-polymer centroid, which most likely 

requires a little bit of coding. 

Best, 

Thomas Kühne

Am 30.05.2019 um 10:16 schrieb Webb Foo <lta...@gmail.com>:

Hello everyone,

Can you explain me how to estimate the free energy profile from a pimd simulation, like constrained MD?

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==============================

Thomas D. Kühne

Dynamics of Condensed Matter

Chair of Theoretical Chemistry

University of Paderborn

Warburger Str. 100

D-33098 Paderborn

Germany

tdku...@mail.upb.de

+49/(0)5251/60-5726

[Webb Foo]

Hi Thomas,

Thanks for your reply. And I'll have a try.

Cheers,

Webb

在 2019年5月31日星期五 UTC+8上午4:52:40，tkuehne写道：

Dear Webb Foo, 

using constrained MD the free energy profile can be computed in terms of the potential of mean force by means of the ensemble 

average of the Lagrange multipliers to constrain your reaction coordinate. You will find a particular good description in the SI of

the following paper: https://www.pnas.org/content/104/8/2626.short

However, when using PIMD, in my opinion the constraint has to be enforced on the ring-polymer centroid, which most likely 

requires a little bit of coding. 

Best, 

Thomas Kühne

Am 30.05.2019 um 10:16 schrieb Webb Foo <lta...@gmail.com>:

Hello everyone,

Can you explain me how to estimate the free energy profile from a pimd simulation, like constrained MD?

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[Christoph Schran]

Dear Webb Foo,

centroid constraints/restraints have been implemented recently and will be available in the upcoming new CP2K release v7.1.

The input is very similar to normal MD simulations. I would recommend using the exact integrator in combination with the PILE thermostat.

Example inputs (which need to be adapted carefully) can be found under tests/Pimd/regtest-1 and regtest-2: h2o_pint_constraints_exact.inp for the constraints and w512_pint_pile.inp for the PILE thermostat.

Note that regtests are usually optimized to trigger as many parts of the code as possible and are not always best simulation practice.

Best, Christoph