Author Topic: optimize geometry  (Read 872 times)

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Offline tara95

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optimize geometry
« on: November 14, 2017, 14:44 »
hi
please  explain to me that,
Is it necessary  to optimize the k-points and cut-off energy parameters before optimize geometry?

Offline Anders Blom

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Re: optimize geometry
« Reply #1 on: November 14, 2017, 14:47 »
Generally yes, and most often the optimization will converge faster if you have sufficient accuracy, because the forces will be more accurate, and the forces are actually more sensitive to settings like k-points than the total energy is. However, sometimes it can save some time to use slightly lower accuracy settings for the first part of the optimization, maybe converge to higher force tolerance like 0.05 eV/A, and then use finer settings to converge the last bit to 0.01 eV/A or so. But the safest option is to ensure good accuracy first, and then run the optimization with that.

Offline tara95

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Re: optimize geometry
« Reply #2 on: November 14, 2017, 15:07 »
thank you :)
Another question;
Which basis set(HGH-FHI-OMX) is more suitable if I use GGA for optimize geometry? And should optimized parameters be used to band structures?

Offline Jess Wellendorff

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Re: optimize geometry
« Reply #3 on: November 15, 2017, 11:04 »
The choice of pseudopotentials+basis set depends in general on the system under investigation. So it's often a matter of testing. Generally speaking, OMX will be better than FHI, but also computationally more demanding. And yes, once you chose a set of parameters, stick to those for subsequent band structure calculation also.

Offline Anders Blom

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Re: optimize geometry
« Reply #4 on: November 15, 2017, 21:34 »
OMX is harder, you need a considerably larger mesh cut-off for those, but I agree they are often (not always) of better quality than FHI.
I would however recommend SG15 as a general-purpose choice.

Offline tara95

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Re: optimize geometry
« Reply #5 on: November 16, 2017, 13:09 »
thank you so much

Offline tara95

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Re: optimize geometry
« Reply #6 on: November 18, 2017, 16:05 »
Hi
This warning  is given in the calculation of the I-V curve device
( the computed multigrid is greater than the required accuracy.
computed residual : 1.07837e-09
Required accuracy  : 1.00000e-12)
 
I do not know what parameters need to be changed now.

Offline Daniele Stradi

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Re: optimize geometry
« Reply #7 on: November 20, 2017, 08:54 »
Hi,
you should increase the density_mesh_cutoff until the error disappears.
Regards,
Daniele.

Offline tara95

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Re: optimize geometry
« Reply #8 on: November 21, 2017, 11:06 »
thank you :)
Another question
In a paper, source and drain regions are heavily doped to be n-type with the density of 1.5×10^13/cm2 for  InSe monolayer,but unit in ATK  is e/atom or e/cm3.Now how do I apply it to the software.

Offline Petr Khomyakov

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Re: optimize geometry
« Reply #9 on: November 21, 2017, 14:43 »
You have to convert the doping concentration of 1.5x10^13 per cm^2 to that per atom in a unit cell, and use the obtained number to set the doping concentration in e/atom in the ATK. 

Offline tara95

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Re: optimize geometry
« Reply #10 on: November 27, 2017, 19:21 »
thank you :)
please explain how to change unit cell of InSe to build armchair and zigzag inse  nanoribbon.

Offline Ulrik G. Vej-Hansen

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Re: optimize geometry
« Reply #11 on: December 14, 2017, 14:10 »
The nanoribbon plugin in the Builder allows you to change the elements, so that would be my suggested way of doing it.