QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: deepwave on October 28, 2012, 03:39

Title: About the bond length of Carbon and Gold in a chain
Post by: deepwave on October 28, 2012, 03:39

in atk tutorials, the bond length of C-C  is 2.9A in a carbon chain, but the actual length is 1.4A. so, i want to know how to set the length in a chain(such as gold(2.88) ) .

Title: Re: About the bond length of Carbon and Gold in a chain
Post by: Nordland on October 28, 2012, 15:54

The carbon chain is a toy system to show spin-polarization of a device. In order for carbon to spin-polarized it needs to be setup in 2.9 Ångstrom distance.
If you follow the tutorial http://quantumwise.com/publications/tutorials/mini-tutorials/94-transmission-spectrum-of-a-spin-polarized-atomic-chain , you
can just enter the lattice constant you want instead of 2.9

Title: Re: About the bond length of Carbon and Gold in a chain
Post by: deepwave on October 28, 2012, 16:34

thank you for you answering. if i set  the bond length to 1.4A, it means that the system is unpolarized? another question occur, how to decision the bond length if i want to use the carbon chain as electrode. in other chain, such as Gold or Iron, whether it need to be set the length longer than its the lattice constant for a spin systems?

Title: Re: About the bond length of Carbon and Gold in a chain
Post by: zh on October 29, 2012, 08:58

Please  do  the total energy of atomic chain as function of the lattice constant of atomic chain in the cases of spin-polarized and non-spin-polarized cases by yourself. The calculations on such systems are quite easy and also quick.

Title: Re: About the bond length of Carbon and Gold in a chain
Post by: deepwave on October 29, 2012, 14:24

thanks for zh:
i have calculate the total energy of carbon chain, the result as follow:
     1.0         1.39         1.4          1.425        1.5           2.0            2.9(A)
-149.029   -155.269   -155.226   -155.097   -154.591   -151.456    -149.227
so i should chose the 1.39(A) for the Carbon chain, right? but why you chose the 2.9? or it will affect the result chose different length?

Title: Re: About the bond length of Carbon and Gold in a chain
Post by: Anders Blom on October 29, 2012, 14:55

The answer was given above: "The carbon chain is a toy system to show spin-polarization of a device. In order for carbon to spin-polarized it needs to be setup in 2.9 Ångstrom distance." We never intended for this calculation to be real in any way. We just want to show how to set up the initial spin, that's all. I don't think it makes much sense to have electrodes made of carbon chains for anything serious. If you want some simple conducting system for electrodes, use a simple metal like Li or a metallic CNT.