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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
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<LI><UL>
<LI><A NAME="tex2html239"
HREF="node10.html#SECTION00043010000000000000">3.3.0.1 Single-point (fixed-ion) SCF calculation</A>
<LI><A NAME="tex2html240"
HREF="node10.html#SECTION00043020000000000000">3.3.0.2 Band structure calculation</A>
<LI><A NAME="tex2html241"
HREF="node10.html#SECTION00043030000000000000">3.3.0.3 Noncollinear magnetization, spin-orbit interactions</A>
<LI><A NAME="tex2html242"
HREF="node10.html#SECTION00043040000000000000">3.3.0.4 DFT+U</A>
<LI><A NAME="tex2html243"
HREF="node10.html#SECTION00043050000000000000">3.3.0.5 Dispersion Interactions (DFT-D)</A>
<LI><A NAME="tex2html244"
HREF="node10.html#SECTION00043060000000000000">3.3.0.6 Hartree-Fock and Hybrid functionals</A>
<LI><A NAME="tex2html245"
HREF="node10.html#SECTION00043070000000000000">3.3.0.7 Dispersion interaction with non-local functional (vdwDF)</A>
<LI><A NAME="tex2html246"
HREF="node10.html#SECTION00043080000000000000">3.3.0.8 Polarization via Berry Phase</A>
<LI><A NAME="tex2html247"
HREF="node10.html#SECTION00043090000000000000">3.3.0.9 Finite electric fields</A>
<LI><A NAME="tex2html248"
HREF="node10.html#SECTION000430100000000000000">3.3.0.10 Orbital magnetization</A>
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<H2><A NAME="SECTION00043000000000000000">
3.3 Electronic structure calculations</A>
</H2>
<H4><A NAME="SECTION00043010000000000000">
3.3.0.1 Single-point (fixed-ion) SCF calculation</A>
</H4>
Set <TT>calculation='scf'</TT> (this is actually the default).
Namelists &IONS and &CELL will be ignored. See Example 01.
<P>
<H4><A NAME="SECTION00043020000000000000">
3.3.0.2 Band structure calculation</A>
</H4>
First perform a SCF calculation as above;
then do a non-SCF calculation with the desired k-point grid and
number <TT>nbnd</TT> of bands.
Use <TT>calculation='bands'</TT> if you are interested in calculating
only the Kohn-Sham states for the given set of k-points
(e.g. along symmetry lines: see for instance
<TT>http://www.cryst.ehu.es/cryst/get_kvec.html</TT>). Specify instead
<TT>calculation='nscf'</TT> if you are interested in further processing
of the results of non-SCF calculations (for instance, in DOS calculations).
In the latter case, you should specify a uniform grid of points.
For DOS calculations you should choose <TT>occupations='tetrahedra'</TT>,
together with an automatically generated uniform k-point grid
(card K_POINTS with option ``automatic'').
Specify <TT>nosym=.true.</TT> to avoid generation of additional k-points in
low symmetry cases. Variables <TT>prefix</TT> and <TT>outdir</TT>, which determine
the names of input or output files, should be the same in the two runs.
See Examples 01, 06, 07,
<P>
NOTA BENE: Since v.4.1, both atomic positions
and the scf
potential are read from the data file so that consistency is guaranteed.
<P>
<H4><A NAME="SECTION00043030000000000000">
3.3.0.3 Noncollinear magnetization, spin-orbit interactions</A>
</H4>
<P>
The following input variables are relevant for noncollinear and
spin-orbit calculations:
<BLOCKQUOTE>
<TT>noncolin</TT>
<BR> <TT>lspinorb</TT>
<BR> <TT>starting_magnetization</TT> (one for each type of atoms)
</BLOCKQUOTE>
To make a spin-orbit calculation <TT>noncolin</TT> must be true.
If <TT>starting_magnetization</TT> is set to zero (or not given)
the code makes a spin-orbit calculation without spin magnetization
(it assumes that time reversal symmetry holds and it does not calculate
the magnetization). The states are still two-component spinors but the
total magnetization is zero.
<P>
If <TT>starting_magnetization</TT> is different from zero, it makes a
noncollinear spin polarized calculation with spin-orbit interaction. The
final spin magnetization might be zero or different from zero depending
on the system.
<P>
Furthermore to make a spin-orbit calculation you must use fully
relativistic pseudopotentials at least for the atoms in which you
think that spin-orbit interaction is large. If all the pseudopotentials
are scalar
relativistic the calculation becomes equivalent to a noncollinear
calculation without spin orbit. (Andrea Dal Corso, 2007-07-27)
See Example 06 for noncollinear magnetism, Example 07
for spin-orbit interactions.
<P>
<H4><A NAME="SECTION00043040000000000000">
3.3.0.4 DFT+U</A>
</H4>
DFT+U (formerly known as LDA+U) calculation can be
performed within a simplified rotationally invariant form
of the <I>U</I> Hubbard correction. Note that for all atoms having
a <I>U</I> value there should be an item in function
<TT>flib/set_hubbard_l.f90</TT> and one in
subroutine <TT>PW/src/tabd.f90</TT>, defining respectively
the angular momentum and the occupancy of the orbitals with
the Hubbard correction. If your Hubbard-corrected atoms are not
there, you need to edit these files and to recompile.
<P>
See Example 08 and its README.
<P>
<H4><A NAME="SECTION00043050000000000000">
3.3.0.5 Dispersion Interactions (DFT-D)</A>
</H4>
For DFT-D (DFT + semiempirical dispersion interactions), see the
description of input variables <TT>london*</TT>, sample files
<TT>PW/tests/vdw.*</TT>, and the comments in source file
<TT>Modules/mm_dispersion.f90</TT>.
<P>
<H4><A NAME="SECTION00043060000000000000">
3.3.0.6 Hartree-Fock and Hybrid functionals</A>
</H4>
<P>
Since v.5.0, calculations in the Hartree-Fock approximation, or using
hybrid XC functionals that include some Hartree-Fock exchange, no longer
require a special preprocessing before compilation.
See <TT>EXX_example/</TT> and its README file.
<P>
<H4><A NAME="SECTION00043070000000000000">
3.3.0.7 Dispersion interaction with non-local functional (vdwDF)</A>
</H4>
See example <TT>vdwDF_example</TT>
and references
quoted in file <TT>README</TT> therein.
<P>
<H4><A NAME="SECTION00043080000000000000">
3.3.0.8 Polarization via Berry Phase</A>
</H4>
See Example 04, its file README,
the documentation in the header of
<TT>PW/src/bp_c_phase.f90</TT>.
<P>
<H4><A NAME="SECTION00043090000000000000">
3.3.0.9 Finite electric fields</A>
</H4>
There are two different implementations of macroscopic electric fields
in <TT>pw.x</TT>: via an external sawtooth potential (input variable
<TT>tefield=.true.</TT>) and via the modern theory of polarizability
(<TT>lelfield=.true.</TT>).
The former is useful for surfaces, especially in conjunction
with dipolar corrections (<TT>dipfield=.true.</TT>):
see <TT>examples/dipole_example</TT> for an example of application.
Electric fields via modern theory of polarization are documented in
example 10. The exact meaning of the related variables, for both
cases, is explained in the general input documentation.
<P>
<H4><A NAME="SECTION000430100000000000000">
3.3.0.10 Orbital magnetization</A>
</H4>
Modern theory of orbital magnetization [Phys. Rev. Lett. 95, 137205 (2005)]
for insulators. The calculation is performed by setting
input variable <TT>lorbm=.true.</TT> in nscf run. If finite electric field
is present (<TT>lelfield=.true.</TT>) only Kubo terms are computed
[see New J. Phys. 12, 053032 (2010) for details].
<P>
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<ADDRESS>
paolo giannozzi
2014-05-28
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