Messages

31

General Questions and Answers / Re: A question about optimization

« on: May 24, 2011, 12:30 »

Your reply is really instructive! In the past, I have used single-zeta polarized to relax the system in order to save the time while calculating the transport properties using double-zeta polarized. So according to what you said, my result may be inaccurate in some way.

I did so because I found the relaxation costs much more time than transport calculation.Is this the usual case? What if the case is that I can afford the transport calculation using double-zeta polarized while relaxation using double-zeta polarized may be too-much time consuming? 

32

General Questions and Answers / Re: A question about optimization

« on: May 24, 2011, 06:54 »

Sorry for poor statement! For the first question, I mean the whole molecule+the region of the tube to which it connects is the subsystem I could use to test the basis set, after that, I use the basis set which combines accuracy and time-efficiency to relax the whole system or I just relax the whole system with the part far away from the molecule constrained?

33

General Questions and Answers / Re: caculation of bloch state

« on: May 24, 2011, 06:14 »

But I got the result that the Z point's bloch state localized on the edge of ribbon when the calculation is not polarized. Is it reasonable?

34

General Questions and Answers / caculation of bloch state

« on: May 23, 2011, 18:46 »

When I calculate the bloch state of zigzag graphene nanoribbon using LDA, I found there is no item of 'none' for spin panel as in the tutorials. what is the problam?
And after I calculated the one spin bloch state of the lowest conduction band at Z, I found the one spin also localized on the edge of ribbon, just as the result using LSDA with the inital setting of edge spin polarizations. Is that right?

35

General Questions and Answers / Re: A question about optimization

« on: May 17, 2011, 08:15 »

1.You mean the choice of the subsystem or the way we relax the entire system? Is it possible the keep choose the range of relaxation in a unit cell constrained in only part of the system ?
2.I don not quite understand the constrain cell choice in the optimization panel,could you explain to me? when it is necessary to uncheck it?
3.Is it necessary to relax system under each bias when calculating the I-V curve?

36

General Questions and Answers / Re: A error

« on: May 17, 2011, 08:01 »

Thanks for your answer and  reference!

37

General Questions and Answers / Re: A error

« on: May 16, 2011, 14:25 »

But I want to compare the properties of bilayer GNR 's dependence for interlayer distance. you mean such interlayer distance is not reasonable for a two layer system? So it is meaningless, right?

38

General Questions and Answers / Re: A question about optimization

« on: May 16, 2011, 14:15 »

But how to choose the subsystem, if the system I am studying is a system with a big molecule conneted with the nanotube, should the subsystem include the whole molecule with unit cell of nanotube or , just just one atom of all the elements in the big molecule is OK？

39

General Questions and Answers / Re: about calculate bandstructure of the graphene nanoribbon

« on: May 16, 2011, 13:57 »

Thanks for your reply! That is really instructive!

40

General Questions and Answers / Re: A error

« on: May 15, 2011, 18:11 »

But could you tell me how to increase the interaction_max_range ?  I find no such parameter in the calculator settings

41

General Questions and Answers / A question about optimization

« on: May 15, 2011, 07:13 »

In the tutorial, the optimization is conducted under the sing zeta basis set to save the time, in practice I have try optimization of a bilayer system consisting of 150 atoms with the single zeta polarized basis set and find the process really time consuming. So is it acceptable to conduct the optimization using simple basis set while conducting analysis using more complex basis set? Optimization under simple basis set will influence the accuracy of the analysis result?

42

General Questions and Answers / A error

« on: May 15, 2011, 06:59 »

I was using ATK to calculate a system consisting of two layers of graphene nanoribbon with the interlayer distance is 8 Angstrom(the script of my model is attached) ,but as the calculation began there is error as follows, could anyone explain to me what is the problam?

                           |--------------------------------------------------|
Calculating Eigenvalues    :

** Back Engine Exception 541 : Diagonalization error, overlap matrix not positive definite, try to increase interaction_max_range
** Location : mathutils.cpp:1123


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