[Wien] Such a vast difference in two values of K’ for the same case.

[Vinayak Mishra]

I have basically two questions to ask. I will like to mention that I
have gone through the related previous questions and their answers on
registered users site. I will be highly obliged if you could kindly
spare some time to go through the following two queries.

1.) I was doing c/a optimization at five different volumes in bct
structure for a particular case and was trying to get equilibrium
volume and tentative value of bulk modulus and its pressure
derivative. I gave optimization for one set of 5 volumes, say  +5.0,
0.0, -5.0, -10.0, -15.0 and another set, say  +5.5, 0.5, -5.5, -10.5,
-15.5  and then get EOS, then I find that there is a huge difference
in the value of pressure derivative of bulk modulus K’ for the two
cases. I have plotted both the cases together in the plot.ps file
attached herewith. Here in the plot ‘E’ is the same constant value of
energy for both the curves. Only thing is, for the sake of clarity of
seeing the two curves together, in the solid curve 0.001 Ryd of energy
is added so that it is shifted up by that much energy so that one can
see the difference between the shape of two curves clearly. Both the
curves as such don’t seem to be much different, then why  such a large
difference in K’. Even otherwise also, why should it matter  whether
the run is given for 1st set of volumes or the 2nd set of volumes.
Could you please comment on this Prof. Blaha?

2.)While doing a spin-orbit calculation, we need to increase Emax upto
10 Ry in case.in1 file even though we are interested in eigenvalues
near Fermi energy. But as said in users guide, in the
"second-variation" these high eigenstates  form the basis functions
for the SO calculation. Without these high eigenvalues there will be a
poor basis even for states near Fermi energy.. But these high
eigenvalues are giving large QTL-B value of 980 or 1500 value, at high
energies say around 4.0 in case.output2 file if emax is set as 5.0
(instead of the default value 1.5) in case.inso file also apart from a
Emax=5 (default in SO calculations) in case.in1 file, when we try to
calculate partial charges by giving the command 'x lapw2 -so -qtl'.
After this, the command 'x tetra'  is given to get density of states.
So as said earlier, this is so when case.inso file also has emax = 5.0
i.e the maximum energy for which output eigenvectors and eigenenergies
will be printed (p.96 of users guide). But if we put emax =1.5, which
is the default value in case.inso file, then anyway at high energies
no computation of eigenvectors and eigen energies is done and no such
statement appears in the case.output2 file. It is true that fermi
energy is far below the energy level at which high QTL-B is quoted in
case.output2 file. My question here is: How and where Emax = 5.0 of
case.in1 file is used so that getting large qtl-b in output2 while
calculating partial charges, is meaningless or unharmful, if we happen
to keep emax equal to 5.0 in case.inso also. I just want to confirm
that a large qtl-b value at energies 0.5 to 1Ryd higher than Fermi
energy in case.output2 file is harmless and that I can use Emax upto
10 in case.in1 file without any hesitation. I will highly appreciate
your clarification on this.

Thank you very much in advance for your attention and time.

V. Mishra
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