[Wien] Graphite NMR chemical shifts

Wed Mar 26 02:04:39 CET 2014

Hi,
TEMP option in in2 if for getting Fermi energy correct in weight files, when TETRA is used 0.5 Ry is added to it.
This should be cleared in the future.

kbT appears only in NMR code when first order perturbation of the occupied wave functions are computed,
to avoid problems related to vanishing gap between empty and occupied states. You are not force to use
-kbT or -metal options, but then k-point convergence for metallic systems may be difficult. Those options were
introduce only to improve the convergence in such cases, but if you use them you should test their effect
on the final numbers. -metal option triggers the smearing with default kbT=5.0d-3. -kbT overrides the default
value with  user specified one.

regards

Robert

On 25 March 2014 PM 5:06:47 Jing-Han Chen wrote:
> Hi,
>
>   I have a further question on the metal option and temperature
> broadening in case.in2. As I follow from the discussion, we have to
> specify TEMP in case.in2 and kbT option for metallic system. I think I
> have a little confusion about this two settings. Is the physical
> meaning and unit (in Ry) of kbT option the same as TEMP in case.in2?
> Why can I not specify only one of this if so?
>
> 2014-03-19 19:47 GMT-05:00 Robert Laskowski <rolask at ihpc.a-star.edu.sg>:
> > Hi,
> >
> > No it does not include Knight shift. Those you can calculate via SCF with external magnetic field.
> >
> > regards
> >
> > Robert
> >
> >
> > On 19 March 2014 PM 12:01:00 Joseph H. Ross Jr. wrote:
> >> I have a followup question on the -metal option in the NMR calculation. My guess is that this option brings up some code to find the fermi surface and better identify which states are filled or empty, prior to the chemical shift calculation. Is that right, or does this option also add in a contribution of the paramagnetic (Knight shift) contribution?
> >> Thanks for the help.   -Joe Ross
> >>
> >>
> >>
> >> On Mar 10, 2014, at 9:07 AM, Robert Laskowski wrote:
> >>
> >> > Hi,
> >> >
> >> > if you have metalic case use x_nmr -metal, and TEMP fermi method in in2 (for
> >> > TETRA Fermi level is incorrect in weight files), You may play with -kbT obtion
> >> > for x_nmr (temperature smearing). This may help, however, metals are difficult
> >> > to converge.
> >> >
> >> > regards
> >> >
> >> > Robert
> >> >
> >> > On 10 March 2014 PM 6:21:34 Jose Barquera wrote:
> >> >> Dear Wien2k users,
> >> >>
> >> >> I have calculated NMR chemical shifts for several crystals and I have
> >> >> not had any problem but in the case of graphite something is going
> >> >> wrong. The chemical shift it is not converging with the number of k
> >> >> points. The value of the chemical shift goes up and down and in some
> >> >> cases it just explode. For example: with 33 x 33 x 10 k points the
> >> >> values is 4896 ppm while with 26 x 26 x 8 k points the value is 44 ppm
> >> >> what it is closer to the expected value.
> >> >> I had used 120000 (72 x 72 x 22) k points and it still not converge.
> >> >> I had notice that depending in the number of k points some times it
> >> >> converge to a insulator configuration and sometimes to a metallic one.
> >> >> When it converge to an insulator configuration the chemical shift is
> >> >> closer to the experimental value.
> >> >> I am using PBE functional but I have also try PBEsol and TPSS without
> >> >> success.
> >> >> Any idea in what could be the problem?
> >> >> Thanks
> >> >>
> >> >> kind regards
> >> >> Jose
> >> >>
> >> >> _______________________________________________
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> >> >
> >>
> >> -------------------------
> >> Joseph H. Ross Jr.
> >> Professor
> >> Department of Physics and Astronomy
> >> Texas A&M University
> >> 4242 TAMU
> >> College Station TX  77843-4242
> >> 979 845 3842 / 448 MPHY
> >> jhross at tamu.edu / http://faculty.physics.tamu.edu/ross
> >> -------------------------
> >>
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> > --
> > ==================================================
> > Dr. Robert Laskowski
> >
> > Senior Scientist, Materials Science & Engineering Department
> > Institute of High Performance Computing, A*STAR
> > 1 Fusionopolis Way, #16-16, Connexis, Singapore 138632
> > Tel(Off): +65. 64191493     Fax: +65. 64632536
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--
==================================================
Dr. Robert Laskowski

Senior Scientist, Materials Science & Engineering Department
Institute of High Performance Computing, A*STAR
1 Fusionopolis Way, #16-16, Connexis, Singapore 138632
Tel(Off): +65. 64191493     Fax: +65. 64632536
=================================================

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