Messages

1

General Questions and Answers / Non-vanishing transmission spectrum in gap region of MoS2 monolayer

« on: June 10, 2022, 22:02 »

Hello, QATK community! Recently, I found out about the TransmissionSpectrum Analysis tool and wanted to plot the transmission coefficient T(E) of a perfect MoS2 monolayer, having in mind trying to place some defects in it later. I followed the tutorials and switched from (optimized) hexagonal unit cell (3 atoms) to orthorhombic (6 atoms) propperly but, when calculating  the spectrum (employing HSE06 functional), I do not get the same result as in the mentioned tutorial, but a similar curve that shows an offset of 2.4 transmission units with respect to that shown in the tutorial, aprox. This means that the transmission value T(E)  is about 2.4 in the entire gap region. I repeated the same calculation using PBE functional and got the same problem. Is there anything I'm not aware of?

I know that T(E) is a sum of transmission coefficients all across the irreducible Brillouin zone, so I guess it is not wrong that those values exceed 2, but it should be 0 in the gap due to non-availability of states with the corresponding energy range, right?

Thanks in advance!

2

General Questions and Answers / Re: optB88 density functional in QATK

« on: June 10, 2022, 21:48 »

Thank you very much for your answer, sir!

3

General Questions and Answers / optB88 density functional in QATK

« on: April 10, 2022, 00:56 »

Hello, QATK community!
I hope I haven't posted on the wrong place. I was comparing some QATK capabilities on a MoS_2 bilayer system, trying to take into account van der Waals forces in order to predict some layer properties. Following many references, I wanted to try optB88. According to the reference given in QATK manual, its exchange part has one parameter, so I guess the corresponding exchange functional is OneparameterB88, right? What about the correlation part? If I'm right, it consists of a local LDA part and a nonlocal part (the most important for vdW in this case, I guess). I noticed there's an available correlation functional named Becke88DionVanDerWaals, but I don't think that's the good one, because it cannot reach convergence (9x9x1 k points and 55 H density-mesh cutoff). Which one would make the famous complete optB88?
Thanks in advance!