Electric field gradient tensor from quadrupole moment script-reg

[GJK]

Hi,
We have the script provided by Dr.Anders http://quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.electrondifferencedensity.html
for finding quadrupole.

The script is for finding qzz(electric field gradient) for a complete system.Is it posssible to provide a quadrupole script for finding qzz on independent atoms in a system.If you could provide we can compute NQR through ATK wonderfully.

I have raised the question for NQR-qzz; but the answers came for finding qzz through other software packages.That time I was completely shielded off from Dr.Anders beautiful script for monopole,dipole and qudrupole.With the existing script we have quadrupole calculation for complete system but not independent atoms.

Thanks in advance

[zh]

1. The default calculator in ATK-DFT module uses the norm-conversing pseduopotential, which doesn't provides the charge density of core electrons. To restore the charge density of core region, additional computational techniques are needed, as done in the  GIPAW package (http://www.gipaw.net/theory.html).
2. The example demonstrated in http://quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.electrondifferencedensity.html is done for the estimation of monopole, dipole, and quadropole of a molecule. But for such calculations for a bulk system without vacuum region, some caution should be taken care of because  the position operator is ill-defined in periodic systems.

[GJK]

Dear Zh ,

Thanks for the reply.But here is the usage exampe http://www.sciencedirect.com/science/article/pii/S0749603612001449
where they have calculated EQR on independent atoms. ATK  is a powerful tool then why not we? Also already as per the advice of Dr.Anders I have tried for convergence tests in molecule and bulk configurations which gave approximately the same results...

I have some clues; you said it is difficult to compute the charge density of independent core region.My question: Is it possible to use the Mulliken report for the excess charges on each atom and compute volume charge density as excess charge on each atom divided by volume occupied by each atom.

We have total volume for the bulk configuration how to compute volume on each atom???

Then we get EFG tensor on each atom.Am I correct???

[GJK]

1. The default calculator in ATK-DFT module uses the norm-conversing pseduopotential, which doesn't provides the charge density of core electrons. To restore the charge density of core region, additional computational techniques are needed, as done in the  GIPAW package (http://www.gipaw.net/theory.html).
2. The example demonstrated in http://quantumwise.com/documents/manuals/latest/ReferenceManual/index.html/ref.electrondifferencedensity.html is done for the estimation of monopole, dipole, and quadropole of a molecule. But for such calculations for a bulk system without vacuum region, some caution should be taken care of because  the position operator is ill-defined in periodic systems.

Dear sir,

If this is the answer then what does the quarupole moment calculated through ATK signify???
Is it the field gradient tensor for the entire molecule???

[zh]

Suggest you read the following paper to understand the basic background of using pseudopotential  for the calculation of NMR, Electric Field Gradient (EFG), and so on:
http://www.tcm.phy.cam.ac.uk/~jry20/gipaw/emr.pdf

" what does the quarupole moment calculated through ATK signify?"
It is calculated only by taking  into account the charge density of valence electrons of whole system.

The reliability of the use of only the valence charge density for the EFG isn't high. Additional contributions should be taken into account, as discussed in the above reference.

In the reference paper as you mentioned,  the nuclear quadrupole resonance was calculated by the Gaussian code, which explicitly treats the core electron density.