CoupledCHAC + WBM nucleation model - parameters question

[Irene Moreno]

Hi all, 

I was wondering if someone could help me out in understanding the meaning behind some of the parameters used in the nucleation and in the CHAC apps. 

First, about the definition of the solubility as used in the calculation of the nucleation probability (which in the code is the variable "calmin"), and how it interacts with the equilibrium composition that comes from the free energy curve. Essentially, should the value of calmin be fixed and equal to the value of the equilibrium composition that is determined by the free energy curve, when defining the free energy as in the CHAC app?

Also, may I ask what are the variables center1, center2 and radius1, radius2 used for, as well as the "order parameter cutoff value?"

Thank you! 

Kind regards,

Irene

[David Montiel]

Hello, Irene

Please see my inline replies below

Let me know if you have any other questions, 

Best,

David

On Fri, Sep 20, 2024 at 3:28 PM Irene Moreno <ire.more...@gmail.com> wrote:

Hi all, 

I was wondering if someone could help me out in understanding the meaning behind some of the parameters used in the nucleation and in the CHAC apps. 

First, about the definition of the solubility as used in the calculation of the nucleation probability (which in the code is the variable "calmin"), and how it interacts with the equilibrium composition that comes from the free energy curve. Essentially, should the value of calmin be fixed and equal to the value of the equilibrium composition that is determined by the free energy curve, when defining the free energy as in the CHAC app?

In the nucleation application, calmin is the concentration at the minimum of the free energy curve for the parent (alpha) phase which, for the free energy curves employed, coincides with the equilibrium concentration of that phase. I want to stress that the equilibrium concentration and the minimum concentration are not the same in general. This only applies if the minima of the free energy curves are at the same height. 

The value that you should use for the probability calculation should be the equilibrium composition of the parent phase. So, the answer to the second part of your question is yes.

Also, may I ask what are the variables center1, center2 and radius1, radius2 used for, as well as the "order parameter cutoff value?"

In the coupledCahnHilliardAllenCahn app, center1, center2 and radius1, radius2 are the centers and the radii of the two circles used for the initial conditions.

The "Order parameter cutoff value" is the minimum allowed value of the sum of all nucleating variable fields where nucleation is allowed to occur. It is implemented to prevent nucleation inside already nucleated particles. See the "Shared Nucleation Parameters" section in this page for more details.

 

Thank you! 

Kind regards,

Irene

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