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<H2><A ID="SECTION00051000000000000000">
4.1 Single-<B>q</B> calculation</A>
</H2>
<P>
The phonon code <TT>ph.x</TT> calculates normal modes at a given <B>q</B>-vector,
starting from data files produced by <TT>pw.x</TT> with a simple SCF calculation.
NOTE: the alternative procedure in which a band-structure calculation
with <TT>calculation='phonon'</TT> was performed as an intermediate step is no
longer implemented since version 4.1. It is also no longer needed to
specify <TT>lnscf=.true.</TT> for <!-- MATH
${\bf q}\ne 0$
-->
<IMG STYLE="height: 1.52ex; vertical-align: -0.55ex; " SRC="img1.png"
ALT="$\bf q$">≠ 0.
<P>
The output data files appear in the directory specified by the
variable <TT>outdir</TT>, with names specified by the variable
<TT>prefix</TT>. After the output file(s) has been produced (do not remove
any of the files, unless you know which are used and which are not),
you can run <TT>ph.x</TT>.
<P>
The first input line of <TT>ph.x</TT> is a job identifier. At the second line the
namelist <TT>&INPUTPH</TT> starts. The meaning of the variables in the namelist
(most of them having a default value) is described in file
<TT>Doc/INPUT_PH.*</TT>. Variables <TT>outdir</TT> and <TT>prefix</TT>
must be the same as in the input data of <TT>pw.x</TT>. Presently
you can specify <TT>amass(i)</TT> (a real variable) the atomic mass
of atomic type <I>i</I> or you can use the default one deduced from the
periodic table on the basis of the element name. If
<TT>amass(i)</TT> is not given as input of <TT>ph.x</TT>, the one given as
input in <TT>pw.x</TT> is used. When this is <TT>0</TT> the default one is used.
<P>
After the namelist you must specify the <B>q</B>-vector of the phonon mode,
in Cartesian coordinates and in units of 2<I>π</I>/<I>a</I>.
<P>
Notice that the dynamical matrix calculated by <TT>ph.x</TT> at <IMG STYLE="height: 1.52ex; vertical-align: -0.55ex; " SRC="img1.png"
ALT="$\bf q$"> = 0 does not
contain the non-analytic term occurring in polar materials, i.e. there is no
LO-TO splitting in insulators. Moreover no Acoustic Sum Rule (ASR) is
applied. In order to have the complete dynamical matrix at <IMG STYLE="height: 1.52ex; vertical-align: -0.55ex; " SRC="img1.png"
ALT="$\bf q$"> = 0
including the non-analytic terms, you need to calculate effective charges
by specifying option <TT>epsil=.true.</TT> to <TT>ph.x</TT>. This is however not
possible (because not physical!) for metals (i.e. any system subject to
a broadening).
<P>
At <IMG STYLE="height: 1.52ex; vertical-align: -0.55ex; " SRC="img1.png"
ALT="$\bf q$"> = 0, use program <TT>dynmat.x</TT> to calculate the correct LO-TO
splitting, IR cross sections, and to impose various forms of ASR.
If <TT>ph.x</TT> was instructed to calculate Raman coefficients,
<TT>dynmat.x</TT> will also calculate Raman cross sections
for a typical experimental setup.
Input documentation in the header of <TT>PHonon/PH/dynmat.f90</TT>.
<P>
See Example 01 for a simple phonon calculations in Si, Example 06 for
fully-relativistic calculations (LDA) on Pt, Example 07 for
fully-relativistic GGA calculations.
<P>
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