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<H2><A ID="SECTION00055000000000000000">
4.5 Calculation of electron-phonon interaction coefficients with the tetrahedron method</A>
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<P>
When you perform a calculation of electron-phonon interaction coefficients
with the tetrahedron method,
you have to use an offset <I>q</I>-point grid in order to avoid a singularity
at <I>q</I> = <I>Γ</I>; you can perform this calculation as follows:
<P>
<OL>
<LI>Run <TT>pw.x</TT> with <code>occupation = "tetrahedra_opt"</code> and <code>K_POINT automatic</code>.
</LI>
<LI>Run <TT>ph.x</TT> with <code>lshift_q = .true.</code> and <code>electron_phonon = ""</code> (or unset it)
to generate the dynamical matrix and
the deformation potential (in <code>_ph*/{prefix}_q*/</code>) of each <I>q</I>.
</LI>
<LI>Run <TT>ph.x</TT> with <code>electron_phonon = "lambda_tetra"</code>.
You should use a denser <I>k</I> grid by setting <code>nk1</code>, <code>nk2</code>, and <code>nk3</code>.
Then <code>lambda*.dat</code> are generated; they contain <!-- MATH
$\lambda_{q \nu}$
-->
<I>λ</I><SUB>q<I>ν</I></SUB>.
</LI>
<LI>Run <code>alpha2f.x</code> with an input file as follows:
<PRE>
&INPUTPH
! The same as that for the electron-phonon calculation with ph.x
:
/
&INPUTA2F
nfreq = Number of frequency-points for a2F(omega),
/
</PRE>
Then <I>λ</I>, and <!-- MATH
$\omega_{\ln}$
-->
<I>ω</I><SUB>ln</SUB> are computed and they are printed to the standard output.
<!-- MATH
$\alpha^2F(\omega)$
-->
<I>α</I><SUP>2</SUP><I>F</I>(<I>ω</I>) and (partial) phonon-DOS are also computed;
they are printed to a file <I>prefix</I><code>.a2F.dat</code>.
</LI>
</OL>
<P>
There is an example in <code>PHonon/example/tetra_example/</code>.
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