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Dear pwscf users,<br>
<br>
I am trying to perform spin-polarized calculations using pwscf,
following the tutorial for LSDA found here: <a
class="moz-txt-link-freetext"
href="http://www.fisica.uniud.it/%7Egiannozz/QE-Tutorial">http://www.fisica.uniud.it/~giannozz/QE-Tutorial</a>.
Unfortunately, I am puzzled by several problems.<br>
<br>
<b>Q1. </b><b>Can pwscf perform spin-polarized calculations using
GGA functionals?</b><br>
I know this seems to be a stupid question, since spin-polarized GGA
calculation should be one of the basic capabilities of an <i>ab
inition </i>program. I checked the mannual for pwscf
(INPUT_PW.html), and found that "npsin=2" enables "LSDA". Also, in
the tutorial mentioned above, it reads "This approach goes under the
name of Local Spin-Density Approximation, or LSDA, even when the
functional E xc is based not on LDA but on GGA". I guess pwscf can
do such calculations, but not convinced.<br>
<br>
<b>Q2. Why the results of "fixed magnetization</b><b>" and "</b><b>Unconstrained
magnetization" are not consistent?</b><br>
In the tutorial I read that there are two approaches to optimizing
the magnetization. One is to vary the tot_magnetization mannually
and to find the minimum of total energy, while in the other approach
the total magnetization is determined during scf calculation by
pwscf automatically. I tried both approaches for bulk silicon and
magnisium oxide, which should be both non-magnetic, and found both
approaches predicted non-magnetic groud state. However, for a 2x2x2
super cell of MgO dopped with one atom of Sc(scandium), the fixed
magnetization approach predicted the total magnetization should be 1
bohr, while unstrained approach predicted it to be ~0.80. What's
more, the value of smearing also affects the total magnetization for
the second approach. Why are not they consistent? Which one should I
trust?<br>
<br>
<b>Q3. </b><b>How to specify starting_magnetization(i)?</b><br>
Are there any tricks to specify reasonable starting_magnetization
for different atomic species? Perhaps the magnet momentum of an
isolated atom is a good guess, but how to relate it to
starting_magnetization? I guess that they are related by the
equation "starting_magnetization = (nelec_spin_majority -
nelec_spin_minority) / nelec_total", since for all spin-up case
starting_magnetization is 1.0 and for all spin-down case it is -1.0.
But I am not sure.<br>
<br>
<b>Q4. Should total magnetization always be intergers?</b><br>
As mentioned in Q2, the total magnetization is fractional when
unstrained magnetization approach is used. Since each electron
carries one bohr of magneton, should the total magnetization always
be integers?<br>
<br>
All suggestions are appreciated.<br>
<br>
Best,<br>
Yunhai Li<br>
<br>
Department of Physics, Southeast University<br>
Nanjing, Jiangsu Province, P.R.C.<br>
<br /><br />
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