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<H2><A ID="SECTION00052000000000000000">
4.2 Memory requirements</A>
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<P>
A typical self-consistency or molecular-dynamics run requires a maximum
memory in the order of <I>O</I> double precision complex numbers, where
<P><!-- MATH
\begin{displaymath}
O = m M N + P N + p N_1 N_2 N_3 + q N_{r1} N_{r2} N_{r3}
\end{displaymath}
-->
</P>
<DIV ALIGN="CENTER">
<I>O</I> = <I>mMN</I> + <I>PN</I> + <I>pN</I><SUB>1</SUB><I>N</I><SUB>2</SUB><I>N</I><SUB>3</SUB> + <I>qN</I><SUB>r1</SUB><I>N</I><SUB>r2</SUB><I>N</I><SUB>r3</SUB>
</DIV><P></P>
with <I>m</I>, <I>p</I>, <I>q</I> = small factors; all other variables have the same meaning as
above. Note that if the <I>Γ</I> -point only (<I>k</I> = 0) is used to sample the
Brillouin Zone, the value of N will be cut into half.
<P>
For hybrid DFTs, additional storage of <I>O</I><SUB>x</SUB> double precision complex
numbers is needed (for Fourier-transformed Kohn-Sham states), with
<!-- MATH
$O_x = x N_q M N_1N_2N_3$
-->
<I>O</I><SUB>x</SUB> = <I>xN</I><SUB>q</SUB><I>MN</I><SUB>1</SUB><I>N</I><SUB>2</SUB><I>N</I><SUB>3</SUB> and <I>x</I> = 0.5 for <I>Γ</I> -only
calculations, <I>x</I> = 1 otherwise.
<P>
The memory required by the phonon code follows the same patterns, with
somewhat larger factors <I>m</I>, <I>p</I>, <I>q</I>.
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