Messages

136

General Questions and Answers / What's the difference of Small electrode and Big electrode ?

« on: November 22, 2009, 04:19 »

Dear, I have one question:

We  test the I-V of  the center region, If we chose different electrodes, we will get different answers. For example lih2li modle,  we want to get the I-V of H2, so we can use the single Li atom as the electrode as the example said ,and we can  also use a big Au(3*3) electrode,  different electrodes will get different answers  cost different calculation time.
which one is better ?

Thank you.

137

Scripts, Tutorials and Applications / Re: Relaxation under bias

« on: October 15, 2009, 11:46 »

Dear Sr,
 
       I am very interested in electromigration, and could you tell me where can find the theoretical basis about the script you updated ? Or which book mentioned this basis ?

Thank you very much.

138

General Questions and Answers / Re: what does "stacking fault" mean ?

« on: October 9, 2009, 04:32 »

problem solved .The reason is the Au( 1 1 1) sruface is stacked as ABCABC, so the surface layers must be 3n.

139

General Questions and Answers / what does "stacking fault" mean ?

« on: October 9, 2009, 04:05 »

I make a two probe configuration as below (attachment 1), the details are: Au(1 1 1), surface vector is 4*4, left and right layers are both 3.
When setting Layers with 2, it shows "stacking fault , Second order matrix element will be ignored ", when setting layers with 3, it shows " Second order matrix elements will be ignored "
My question are: what does stacking fault mean, and this configuration with 2 layers is ok ?
                        I noticed that the structure detail of two Probe is different with 2 and 3 layers (attachment 2 ), why? Any rules should be notice when setting the TwoProbe configuration ?

140

General Questions and Answers / Configuration like this is ok ?

« on: October 8, 2009, 14:11 »

Dear,

     I want to get the I-V characteristics of Cu nanowires, and make this configuration :the electrodes are Au(1 1 1), and the Cu nanowires comes from other literature.  I want to know:
    1,  Is this configuration ok ?
    2,  If it's ok, anything special settings during calculation should be noticed ?
 
   

141

Scripts, Tutorials and Applications / Re: Relaxation under bias

« on: August 9, 2009, 14:11 »

Thanks you for your replies, and I still have Two more questions:

First,after reading this reply, I still confused how to do geometry optimization of a two-probe system under bias, especially  "5) One can consider adding functionality for initializing the finite bias relaxation from a zero-bias converged density matrix. This requires a few more lines of code, but shouldn't be a huge task. It can sometimes be hard to converge a finite bias calculation from scratch, so we might need this... Post a reply here if you need that feature!"  Could you give an example or scripts about how to do it .

Second,  should I use the geometry configuration optimized under finite bias or the geometry configuration optimized under 0 bias, to calculate other properties, such as DOS.

Thank you.

142

General Questions and Answers / How to calculate the bond force and bond length under different bias

« on: July 29, 2009, 16:29 »

In this article http://prola.aps.org/abstract/PRB/v67/i19/e193104 (PRB 67, 193014, 2003) , the author did calculations using Siesta and got the Band force , Overlap population , and the Relaxed bond length under different bias .

We meet 2 questions when repeat this work by ATK .
1. How can we get the different band length under different bias ? In the article mentioned above , the author got the relaxed bond length and bond forces under different bias. I checked the ATK manual, didn’t find relevant command or ways to get such a result . Did the author used Siesta and  some other kind of software to accomplish this task  or just the ATK  could  bring this job to success ?
2.What is command CalculateAtomicForces used for ? Could we use it to calculate the atom force under different bias ?
I did some tests using the lih2li example in ATK. First , we did the Geo_Opt.
(The parameters :  froce tolerance is 0.05eV/Ang, Kpoint (1, 1 ,500 ) , basis set is DZP). Second , we set the Electrod Voltages (0, 0.1, 0.3 , 0.5 V) to calculate the relevant AtomicForces and Mulli_Popu and got the datas as below .
Bias (V)   Fz 1 (0.1eV/Ang)    Fz 2 (0.1eV/Ang)   Mulli population1    Mulli population2
0   -2.02               2.02                    1.0065   1.0065
0.1   -2.01               1.94                    1.0082   1.0045
0.3   -2.00               1.80                    1.0113   1.0011
0.5   -1.98               1.66                    1.0139   0.9983
The Fz 1 and Mulli_Popu1 are the force and Mulli_popu on H1 , the same to H2.  

Moderator edit: band->bond not to confuse anyone

143

General Questions and Answers / How to analysis CalculateAtomicForces

« on: July 19, 2009, 07:40 »

I used the usage example, on page 285 in the manual, to test how to use CalculateAtomicForces, and got this answer:

     Fx             Fy             Fz
o    -0.0247      -0.0319       0
h    0.0308      0.0013          0
h    -0.0064       0.0303        0

As for the whole h2o, the sum of these forces is ok, but for an certain atom, it is not like that. How to analysis the answer?　And, I want to use CalculateAtomicForces to measure an certain atom in TwoProbeSystem under different bias, is that ok? Thanks for your answer.