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QuantumATK => General Questions and Answers => Topic started by: beauyy on July 7, 2015, 03:00

Title: optomization of monolayer silicene device
Post by: beauyy on July 7, 2015, 03:00

Dear sir,
     I have built the bulk of monolayer silicene and optimized it according to http://www.quantumwise.com/publications/tutorials/item/512-opening-a-band-gap-in-silicene-and-bilayer-graphene-with-an-electric-field. But the devices built from the optimized bulk is difficult to SCF. What is wrong with my device structure and the device optimization?
The attached file is the script for device optimization.

Title: Re: optomization of monolayer silicene device
Post by: beauyy on July 8, 2015, 05:25

Can anybody answer this question?

Title: Re: optomization of monolayer silicene device
Post by: Umberto Martinez on July 8, 2015, 10:32

you should first try to converge at zero bias and only afterwards increase bias by restarting from this state.
This has been discussed various time in the forum, you can search for similar topics.

Title: Re: optomization of monolayer silicene device
Post by: beauyy on July 11, 2015, 05:50

Thanks for your reply.  I find that the structure of monolayer silicene can easily to achieve SCF under lower bias,  but the monolayer silicene is still difficult to achieve SCF under 1.6 V when I use the optimized structure under 1.4 V. What can I do for this problem?

Title: Re: optomization of monolayer silicene device
Post by: Umberto Martinez on July 13, 2015, 10:46

Does a full SCF state converge under high bias?
note that the effect of the finite bias on the geometry optimization is most probably very small and you can use the zero bias geometry for your finite bias calculations.
Since you managed to converge the forces at 1.4 V you can see if the geometry is very much different from the zero bias one.
If indeed they are very similar you can safely use the zero bias geometry.

Title: Re: optomization of monolayer silicene device
Post by: Anders Blom on July 13, 2015, 17:00

There is very, very rarely any significant geometry changes when you apply the bias, so I would advise against trying to optimize the structure for each bias point.

Title: Re: optomization of monolayer silicene device
Post by: beauyy on July 14, 2015, 10:27

The geometric optimization under 1.4 V is easy to achieve full SCF. The geometry is the same to that under zero bias. But when I  do the geometeic optimization  under 1.6 V, it is hard to reach full SCF whatever the original geometry is under zero or 1.4 V. It is a big trouble to me.

Title: Re: optomization of monolayer silicene device
Post by: beauyy on July 17, 2015, 07:42

Is the geometry of monolayer silicence unavailable under the higher bias than 1.4 V ?

Title: Re: optomization of monolayer silicene device
Post by: Umberto Martinez on July 17, 2015, 08:21

As we say, you can safely use the geometry obtained at zero bias.
In order to achieve convergence you can try to increase your k-point sampling.