QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: Anirban Basak on January 7, 2012, 08:43

Title: Relative speed and accuracy of device algorithm, exchange correlation, basis set
Post by: Anirban Basak on January 7, 2012, 08:43

Hi,

        I want to know the relative speed and accuracy of device algorithm (maybe like Recursion > Direct > Krylov), exchange Correlation, basis set for ATK-DFT (device). (especially in the case of I-V characteristics of CNT with various metal contacts). Accuracy is very important.

I'd also like to know whether ATK-device calculates both ballistic transport and diffusive transport. Does not ATK calculate scattering probability from scattering potentials in diffusive transport?

Thank You

Title: Re: Relative speed and accuracy of device algorithm, exchange correlation, basis set
Post by: zh on January 7, 2012, 14:03

The available exchange-correlation functional in ATK-DFT includes the LDA and GGA.  Actually, both of them are the same level. It is difficult to give a definitized suggestion to say which one of them is much better for the problem under your study.  The job for the GGA calculation may somehow slightly heavier than that of the LDA, but usually it can be ignored.

Larger basis set, heavier job and more accurate. In other words,  for accuracy: DZP > SZP > SZ; for speed:  SZ> SZP> DZP

Only the ballistic transport can be calculated, the diffusive transport cannot be.

Title: Re: Relative speed and accuracy of device algorithm, exchange correlation, basis set
Post by: Anirban Basak on January 9, 2012, 00:19

What about the device algorithms? Can you make a relative comparison between Krylov, Direct and Recursion methods?

Title: Re: Relative speed and accuracy of device algorithm, exchange correlation, basis set
Post by: Anders Blom on January 9, 2012, 00:31

The difference is not dramatic, perhaps Krylov is 10% faster, but it depends on the system at hand, what dominates the time consumption. It's not a major point of performance under any circumstance.

Title: Re: Relative speed and accuracy of device algorithm, exchange correlation, basis set
Post by: Anirban Basak on January 15, 2012, 06:39

So. No diffusive transport? Only Ballistic Transport.  :(