[QE-users] Transferred hyperfine coupling constants in TM-oxides

[Kris Harris]

Thanks for the reply and the PP.

I had hoped to get close here given Mali et al. reported such excellent
agreement for this exact system using your code in 2010. Though thanks for
the hint tip that I may not find continued agreement with other systems at
this level of theory.

I tried the alternate PP you sent and get somewhat different results,
though the two calculations are closer to each other than either is to the
experiment.  Perhaps this suggests I am doing something wrong?

The Capsoni paper I mentioned has:
Li1:       A = 4.32 MHz
Li2/Li3: A = 2.13 MHz/ 2.07 MHz  (crystallographically very similar)

Reading chemical shifts from Fig. 4 of Mali et al's Quantum Espresso
calculations and using their Eq. 1  (approximate as magnetic susceptibility
not known) to convert A values yields:
Li1:       delta = 1425 ppm       --> A = 4.14 MHz
Li2/Li3: delta = 800/760 ppm  --> A = 2.33/2.21 MHz (for the 2 sites)

The results I get with this new PP are (Li1 here is the site well-known to
have the larger A value):
     ----- Fermi contact in MHz -----
               bare            GIPAW           core-relax      total
     Li   1       -9.209256        8.650557        0.000000       -0.558699
     Li   2      -12.302726        4.367716        0.000000       -7.935010
     Li   3      -12.374583        4.261266        0.000000       -8.113317

They aren't too sensitive to ecutwfc. Interestingly, the "GIPAW" term is
nearly exactly double the correct answer. I sort-of get the idea of your
core-relaxation theory, but I haven't managed to read anything to
understand the breakdown into the "bare" vs "GIPAW" components.

thanks for any further insight,
Kris

On Wed, Apr 18, 2018 at 7:19 AM, Davide Ceresoli <davide.ceresoli at cnr.it>
wrote:

> Dear Kris,
> the core-relaxation feature of GIPAW is extremely experimental.
> It's based on a perturbation approach which might not be adequate
> in all cases.
>
> Could you try with the attached pseudopotential? this one has 3 valence
> electrons for Li and a cutoff between 120 and 150 Ry should be sufficient.
> This way, the polarization of the 1s electrons should be described at a
> better level.
>
> However, we are also working on similar Li-battery materials, comparing to
> experiments and Crystal14+B3LYP calculations, and in some cases we are
> not able to reproduce the Li hyperfine cc.
>
> Good luck for your calculations.
>
> Davide
>
> --
> ------------------------------
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>
> On 04/17/2018 06:45 PM, Kris Harris wrote:
>
> Hi,
>
> I'm starting out with QE and am attempting to learn by repeating some
> literature results for hyperfine coupling constants for Li in Li2MnO3.
>
> Capsoni et. al in 1997 Phys. Rev. B. list the experimental value for A as
> 4.31 MHz for one site (there are 2 other sites at essentially half that A)
>
> Mali. et al. were able to reproduce that value very well in Chem. Comm. in
> 2010 (DOI:10.1039/c003065a) using QE with the GIPAW module.  I'm attempting
> to reproduce that result, following their method as close as possible.
>
> I used dist.x to attempt to verify the structure, and did some convergence
> tests with respect to ecutwfc and k-points to make sure the calculations
> was reasonable. I also verified that the binary I have reproduced the H2O+
> test case included in the distribution.
>
> The result I get is quite a long ways off (0.06 MHz and -7 MHz instead of
> ~4.3 and ~2.15 MHz).
>
> Any help on what I've managed to do wrong here would be greatly
> appreciated.
>
>
>
>
>
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