Density functional theory (DFT) gives the ground state electronic structure of a system (material). There are packages like QUANTUM ESPRESSO, VASP, etc., that calculates the electronic structure based on the DFT. I am wondering if it is possible to calculate the electronic band structure at a particular temperature in these codes so that the evolution of the band structure with temperature can be seen?
Any kind of help is highly appreciated.
Thank you !
I am more familiar with VASP, but to some extent it is possible to do this. By far the most important effects will be caused by a change in the material's structure as the temperature increases; the lattice parameter will increase, and also the symmetry of the structure may change at certain transition temperatures. For example, perovskites often have a cubic structure at high temperatures, which is replaced during cooling by a lower-symmetry structure with octahedral tilting distortions.
For most problems, I expect including this effect will be enough. If the material is metallic or has a small band gap, there will be some electron excitations that could be modeled with time-dependent DFT perhaps, but this will be a lot of effort and computational cost for a small improvement in accuracy. VASP has a built-in parameter SIGMA which can be used to "smear" the electrons in a similar way to the effects of temperature, but this parameter only exists to improve convergence and I don't think it is meant to capture temperature-dependent physics accurately.
Thank you Steven Hartman for your reply. Similar to VASP, Quantum ESPRESSO also have a smearing parameter called 'degauss', which is used to smear the electrons near the Fermi level. But I am not sure if it is just a convergence parameter or can be considered as the temperature effect on the band structure.
I think band structure is a concept at 0 K temperature. Raising the temperature makes the atoms vibrate and their states are not static anymore.
Thank you Ehsan Moradpur-Tari for the comment. But I think the band structure can exist at temperature T for the corresponding configuration of the system. But I do not know how to calculate theoretically using QUANTUM ESPRESSO.
Dear Sonu Keshri
I think the tempearture dependence of electronic band structure can be found out using Thermo_Pw code which is a post-processing tool integrated with Quantum Espresso package. As this is the code that is used to find out temperature dependence of mechanical/elastic parameters so may be it is also possible to find out the temperature dependence of band structure also.
To calculate and compare the electronic band structure at different temperatures in the QUANTUM ESPRESSO code, you can follow these steps:
It is important to note that the band structure can be affected by various factors such as the choice of exchange-correlation functional, pseudopotentials, and k-point mesh. Therefore, it is recommended to perform convergence tests to ensure the accuracy and reliability of the results.
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