Hi,
I'm pretty familiar with the quantum transport DFT-NEGF method. Therefore, I'm also familiar with the computational costs for moderate system size. I wanted to know if it is acceptable, to calculate the transmission coefficient, DOS and PDOS from a DFT Hamiltonian, or is it necessary (meaning makes a lot of difference in thermal equilibrium) to calculate the Hamiltonian self-consistently using DFT-NEGF.
As far as I understand, DFT-NEGF procedure is used to integrate both equilibrium and non-equilibrium part of the density matrix, and I was wondering if it is necessary to go through the whole DFT-NEGF cycle, if one is calculating the equilibrium (0V) transmission coefficient.
Thanks in advance
Hi, if you are at 0 bias and your electrodes are defined consistent with a supercell calculation (i.e. you do not use wide band approximation and the supercell is large enough that the electrode behaves bulk-like as in NEGF) the results should not change. In both case you should converge to the same Hamiltonian at equilibrium, physically you are describing "almost" (subtleties may be given by the electrodes, as said) the same system.
In fact, I suppose that many DFT based codes which only calculate transmission in linear response do not implement the NEGF integration of density, but rely on equilibrium Green's function as a sort of post-processing.
Once you go beyond linear response in bias, the two formulations will not be equivalent as the non-equilibrium part of the density matrix is not zero, as you correctly point out.
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