Hello all,
I am trying to use DFT to obtain the 'bandgaps' andopical properties of a few quantum dots (QD) I am working on. I know that QD are non periodic and we cannot actually talk about 'bands' but rather about the highest and lowest molecular orbitals. How can we simulate these in DFT? I use Quantum Espresso (QE). I have basically set he input by putting vaccum in all directions, and just using the 'Gamma' point. For those who are familiar with quantum espresso, I even used the flag ' assume_isolated='martyna-tuckerman''.
So far so good. The force on the QD is not small. So I tried relaxing the structure. However, upon relaxation, the whole material was dismantled. I also need to calculate the optical properties.
Any help on how to circumvent this (or any advice) is highly appreciated.
Regards
How did you preoptimize your structure? Did you try a semiempiric method, e.g. PM7 as implemented in Mopac? Was it stable there?
@jurgen. I did not optimize it. My intention was to do that in Quantum Espresso . I just formed the structurw using VMD
Hello,
You have to fix the movement of atoms during relaxation. You can do this by changing the degrees of freedom.
Best Regards,
Enamul
Enamul Haque Thanks for your answer. You mean adding "0 1 0" (for example) at the end of the atomic positions, which instructs the code to keep the x and z coordinates of the atoms intact during relaxation?
Elie Albert Moujaes Its better to use "cell_dofree" option in the &CELL tag. Please see the user guide for details.
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