[Wannier] dist_cutoff, tran_win_min, tran_win_max

[Giovanni Pizzi]

Dear Zeina,

There is no "exact" value for these flags. dist_cutoff sets to zero the hoppings for WF farther than this distance. You can do a bulk calculation, see when the hoppings are sufficiently small, and use that distance as a rough estimate of dist_cutoff. To know if the choice was a good one, try to calculate e.g. the band structure with that dist_cutoff and see if it changes significantly (if it does, the cutoff was too small). As any convergence parameter, it is always a compromise between accuracy and computational cost of the calculation, the larger the better, but also if you do a LCR calculation you will need to take into account larger principal layers and thus you will need to make a more expensive calculation.

For tran_win_min and tran_win_max, these simply identify the energy window range in which you want to calculate the transport. Do a band structure to identify the relevant bands and their energy window, and use that range as a transport energy window. Note that you can always rerun the calculation later with a different window, in case of doubt. The computational cost is in good approximation a constant times the # of energy points you use, so the larger the window, the more points you calculate. In case of doubt, you can take a larger window with a coarser energy grid in a first step (parameter tran_energy_step) and then do a calculation on a finer grid in the energy window of interest.

Looking into examples/tutorials may be of help, see for instance the Santa Barbara school (and the other tutorials, too) here: http://wannier.org/user_guide.html

Best,
Giovanni


--
Giovanni Pizzi
Post-doctoral Research Scientist
EPFL STI IMX THEOS
MXC 340 (Bâtiment MXC)
Station 12
CH-1015 Lausanne (Switzerland)
Phone: +41 21 69 31124




On 18 Nov 2014, at 23:54, Zeina Al-Dolami wrote:

Thanks Dr. Giovanni for your detailed answer. I have another question about dist_cutoff, tran_win_min, and tran_win_max. I know what they represent as they are clarified in the user manual. However, I am confused about their values. My question is are they chosen approximately? or there is a specific way to find their exact values? I have been looking into many references, but none of them is given the answer that I am looking for. It might be explained elsewhere that I am not aware of. Any answer is appreciated as I am still learning how to use wannier90. Looking forward to hearing from you and many thanks in advance

Zeina
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