# Tag Info

13

I concur with the answer by Alone programmer, but his answer only gives half the story. The coefficients or the model parameters come into the picture later and are actually obtained by optimization of both the experimentally obtained and theoretically calculated data. Here I will discuss the experimental data since the DFT part has already been discussed. ...

11

Basically you need to find $L_{ij}^{m}$ coefficients in the Redlich-Kister polynomials from DFT calculations, related to temperature as: $$L_{ij}^{m} = a_{ij}^{m} + b_{ij}^{m} T + c_{ij}^{m} T \ln(T) + d_{ij}^{m} T^{2} + e_{ij}^{m} T^{3} + \frac{f_{ij}^{m}}{T}$$ Typically you need just the values for $m \leq 2$. I think this is a good reference for the ...

8

Thanks to Tyberius for pointing out one issue in the database in their comment. The pycalphad database parser is strict, but also tries to prevent ambiguities or mistakes. I made the following corrections: Changed ELEMENT Y HCP_A3 8.89059+01 5.9664E+03 4.4434E+01 ! to ELEMENT Y HCP_A3 8.89059E+01 5.9664E+03 4.4434E+01 (adding E to the exponent of the mass) ...

6

if you had access to the database equations for a given alloy system, could you analytically solve (and thus solve quickly) for the conditions (i.e., temperatures and compositions) that would produce the phase combination that you desire? Generally, the answer to this question is no. If we knew how to predict which phases were stable analytically without ...

6

In your comment, you mentioned that you may be testing many alloys (100,000s). I will assume that interested in taking more of a screening approach, rather than specifying precisely 100,000 alloys compositions. In that case, it is easy and faster to let pycalphad broadcast the conditions for you. It will skip any conditions that have independent mole ...

5

Thermo-Calc creates new composition sets from the global minimization process and you cannot, to my knowledge, have direct control of preventing certain composition sets from being created. Disabling global minimization (removing .enable_global_minimization()) may get you what you need, but you should be careful to ensure that the composition set of FCC_L12 ...

5

I don't have access to TC-Python, so I can't offer advice on how to use the API specifically. This is more of a workaround than a direct way to get Thermo-Calc to tell you whether the phase is ordered or disordered. Are you able to get the site fractions from an equilibrium calculation? In console mode, you can use the Y(CR,BCC_B2#2) syntax. My understanding ...

5

I am not sure about TC-Python but in console mode, you can access the Gibbs energy equations directly using the Gibbs Energy System (GES) module. In case you need the details about a particular phase then you have to first define the system as usual and then after retrieving the data go to the GES module and use the List_phase_data command. You will have to ...

5

As a retired professor in Computational Thermodynamics I am happy that young students try to use the Calphad methods to understand materials. However, to model a phase using Calphad there are some background needed. A Calphad database is built from a set of data for the pure elements in different phases describing how the Gibbs energy of the element vary ...

4

Thermo-Calc's DGM is the normalized parallel tangent driving force per mole of components. To be able to compute the driving force of a phase, it must be set to "dormant" status so that it cannot become stable, but the driving force can still be computed. Here's an example macro of how this could be done in Thermo-Calc: @@ These commands can be ...

4

Enthalpy and entropy are the temperature dependent terms in free energy from which enthalpy is a dominant term mainly at lower temperature and entropy is dominant at higher temperature (because randomness is more at higher temperature). This temperature effect can be considered by utilizing the heat capacity at constant pressure (Cp). Phonopy code is there ...

Only top voted, non community-wiki answers of a minimum length are eligible