DFT and phase stabily computation

[aihaike]

Dear all,

I'm new in the DFT word and I wish to calculate as a practice the $$\alpha$$/$$\beta$$ quartz phase transition as function of temperature.
For each phases I imaged preforming CPMD simulation for a given temperature range and then calculate the phonon DOS. From the later I should be able to get the free energies.
So I wonder whether there is a "better" or more efficient way the get the Gibbs free energy as function of temperature?
My other issue is about which code to use. I had a look to abinit, bigdft, quantum-espresso and siesta. The point is it require lot of time to actually get use to each of them and then choice the best for you. So, I'd like to have your opening.
There are so many issues to manage (method, codes) that I'm getting stuck.
Thanks in advance.

Eric.

 

[eljose79]

Dear Eric,

Welcome to the world of DFT! Calculating the \alpha/\beta quartz phase transition can be a challenging and time-consuming task, but with the right approach and tools, you can get accurate results. Firstly, I would recommend using a well-established DFT code such as Quantum ESPRESSO or VASP for your calculations. These codes have been extensively tested and have a large user base, making it easier for you to find support and resources. Additionally, they offer a wide range of methods and functionals to choose from, giving you more flexibility in your calculations.

As for efficiency, there are a few things you can do to speed up your calculations. One approach is to use a hybrid functional, such as HSE06, which combines the accuracy of a DFT calculation with the speed of a semi-empirical method. Another option is to use parallel computing, which can significantly reduce the computation time for your simulations.

In terms of calculating the Gibbs free energy as a function of temperature, there are a few methods you can use. One common approach is to use the quasi-harmonic approximation, where you calculate the phonon DOS at different temperatures and then use the Debye model to calculate the free energy. Another option is to use thermodynamic integration, where you calculate the free energy difference between the two phases at different temperatures and then use a thermodynamic cycle to get the Gibbs free energy.

I hope this helps you in your research. Good luck with your calculations!