SCALEE: Difference between revisions

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{{TAGDEF|SCALEE|[real]|1}}
{{TAGDEF|SCALEE|[real]|1}}


Description: This tag specifies the scaling constant of the energies and forces.
Description: This tag specifies the scaling constant (coupling parameter) of the energies and forces.


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In thermodynamic integration the free energy difference between two systems is defined as
In thermodynamic integration the free energy difference between two systems is defined as


<math> \Delta F = \int\limits_{0}^{1} d\lambda \langle U_{1} - U_{0} \rangle </math>
<math> \Delta F = \int\limits_{0}^{1} d\lambda \langle U_{1}(\lambda) - U_{0}(\lambda) \rangle </math>.


where
Here <math>U_{1}(\lambda)</math> and <math>U_{0}(\lambda)</math> describe the potential energies of a fully-interacting and a non-interacting reference system, respectively. The interaction of the constituents within the system is controlled via the coupling parameter <math>\lambda</math>. The {{TAG|SCALEE}} sets the value for the coupling constant.


By default {{TAG|SCALEE}}=1 and scaling of the energies and forces via the coupling constant is carried out. To enable the scaling {{TAG|SCALEE}}<1 has to be specified.


For thermodynamic integration this parameter controls the coupling parameter <math>\lambda</math>.
Two possible options are available for the reference system:
 
This parameter is only used if {{TAG|SCALEE}}<math>\ne</math>1.


*Ideal gas:
Usually the thermodynamic integration is carried out from the ideal gas to the liquid state.
Usually the thermodynamic integration is carried out from the ideal gas to the liquid state.


*Harmonic solid
If the file {{TAG|DYNMATFULL}} exists  in the calculation directory (from a previous calculation using {{TAG|PHON_NSTRUCT}}=-1) and {{TAG|SCALEE}}<math>\ne</math>1, the second order Hessian matrix is added to the force and thermodynamic integration from a harmonic model to a fully interacting system is carried out. Here the Hamiltonian for a certain integration point along the thermodynamic integration pathway is given as
If the file {{TAG|DYNMATFULL}} exists  in the calculation directory (from a previous calculation using {{TAG|PHON_NSTRUCT}}=-1) and {{TAG|SCALEE}}<math>\ne</math>1, the second order Hessian matrix is added to the force and thermodynamic integration from a harmonic model to a fully interacting system is carried out. Here the Hamiltonian for a certain integration point along the thermodynamic integration pathway is given as



Revision as of 09:15, 31 March 2020

SCALEE = [real]
Default: SCALEE = 1 

Description: This tag specifies the scaling constant (coupling parameter) of the energies and forces.


In thermodynamic integration the free energy difference between two systems is defined as

.

Here and describe the potential energies of a fully-interacting and a non-interacting reference system, respectively. The interaction of the constituents within the system is controlled via the coupling parameter . The SCALEE sets the value for the coupling constant.

By default SCALEE=1 and scaling of the energies and forces via the coupling constant is carried out. To enable the scaling SCALEE<1 has to be specified.

Two possible options are available for the reference system:

  • Ideal gas:

Usually the thermodynamic integration is carried out from the ideal gas to the liquid state.

  • Harmonic solid

If the file DYNMATFULL exists in the calculation directory (from a previous calculation using PHON_NSTRUCT=-1) and SCALEE1, the second order Hessian matrix is added to the force and thermodynamic integration from a harmonic model to a fully interacting system is carried out. Here the Hamiltonian for a certain integration point along the thermodynamic integration pathway is given as

Related Tags and Sections

VCAIMAGES, IMAGES, NCORE IN IMAGE1, PHON_NSTRUCT