spinat

structure determination,...

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spinat

Postby Ngeah » Wed Aug 18, 2010 1:58 am

Hello everyone, I am a new student in QM, DFT, and the like, and I'm essentially teaching myself as I go along, so I'd like to pre-emptively apologize for my incompetence.

I was trying to run some spin-polarized calculations. I'm a little confused with how to determine the values for spinat. I know it should be rather trivial, but if someone can point me in the right direction as to where I could read up on this, it would be very much appreciated. Also, is this value just an intial guess that will evolve as the program runs (bad inputs just lead to a longer calculation), or is it imperative that I choose good values right away (bad values yield poor results).

Of course, an explanation would be much appreciated as well.

Cheers
Ngeah
 
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Joined: Wed Aug 18, 2010 1:44 am

Re: spinat

Postby Robin » Thu Aug 19, 2010 3:39 am

Dear Ngeah,

I often choose the initial guesses according to the usual atomic magnetism in other systems. However, this can be incomplete sometimes. In zigzag graphene nanoribbon (ZGNR), although carbon atoms carry no magnetism ordinarily, ZGNR's edges do possess several magnetic configurations. I such case, you need to analyze the system and test your conjectures.

If a system owns several magnetic states, surely one needs to try different initial states to get them. And an initial guess will evolve to its close final state. But if there is only one magnetic state, usually different initial guesses will not differ much in final result and computational time.

Sincerely,
Guangfu Luo
Robin
 
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Joined: Thu Jan 14, 2010 4:18 am

Re: spinat

Postby Ngeah » Thu Aug 19, 2010 8:23 pm

Thank you, Robin for your response. And for AFM calculations, I'm guessing it's safe to assume that I don't have to worry about the sign changing while it evolves. Is this right? Thanks agian.
Ngeah
 
Posts: 7
Joined: Wed Aug 18, 2010 1:44 am

Re: spinat

Postby Robin » Fri Aug 20, 2010 4:51 am

Dear Ngeah,

The spin signs could change in an AFM calculation. If they finally evolved to a state you are looking for, you made a good guess.

Sincerely,
Guangfu Luo
Robin
 
Posts: 61
Joined: Thu Jan 14, 2010 4:18 am

Re: spinat

Postby ham » Fri Jun 17, 2011 12:52 pm

Hello,
how can I choose the spinat parameter for a system with 48 carbon atoms and 6 hydrogen atoms !!
thank you so much
ham
 
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Joined: Wed Mar 03, 2010 4:31 pm


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