what is the meaning total energy derived form SCF convergence using quantum espresso DFT calculations
why the values are negative and huge for some crystalline solids?
Hi,
DFT by construction gives the ground state density and total energy. So the value you see is the total energy, when you use as a reference the energy in the pseudo potentials used by QE. So, per se that value does not have any particular meanin, but it is useful when you start comparing structures or modify your unit cell. As usual in physics the important piece of information are energy differences.
Cheers,
Roberto
Hello Roberto, thanks for your answer. I mean , are those energies can be a reference to compare the thermodynamic stability of two different materials?
It depends. You can compare structures made of the same number of atoms and species. Otherwise the revenue energy will be different. For example if you want to estimate the binding energy of an extra H atom to a given structure you compare:
E(your structure+H)-E(your structure)-E(H) or 1/2E(H2)
on the other hand if you want only to study the different unit cells you can do a direct calculation...
I can say it is the backbone for a calculation to begin with. Means how much k-points to take, the value of energy cut off, etc. All these values are predicted by checking the total energy and then choosinvaluesg the value achievefor which we achive total energy convergence with respect to the parameter we choose. Like convergence of energy wrt no. of k points will tell us how much k-points are sufficient.
Also we can calculate the lattice parameter of a given material just by plotting the variation of total energy wrt to different valeues of lattice values and then look for the value for which total energy is minumum as that will corresponds to ground state.
Roberto D'Agosta Is it possible to calculate the barrier energy (energy required for an H atom to move through MoS2) from the knowledge of the total energy? Or I must do Nudge Elastic Band calculation?
Abhinav Nag
If I have Sc-XRD data and corresponding .cif file of any material, will I have to do lattice parameter optimization before calculating band structure or DOS? Because, if do so, I will get the band structure of the optimized structure, not the actual structure that I have got from experimental .cif file? Please explain.
Abhinav, yours is admittedly an open question and no sure answer are available also inside the community. Some people would recommend using the experimental structure other would go for the optimised structure. Admittedly, if you stop at the band gap you probably get better results from the experimental structure. But if you want to calculate also binding energies and structural factors, you must go for the optimised structure. This boils ultimately down to the fact that DFT isn't designed to give you the band structure or the bandgap.
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