orrelation
functional is defined as the local density approximation (LDA) for
closed shell systems and its counterpart the local spin-density (LSD)
approximation for open shell systems.  Within this approximation the
exchange functional is the Slater <IMG
 WIDTH="32" HEIGHT="36" ALIGN="MIDDLE" BORDER="0"
 SRC="img107.gif"
 ALT="$\rho^{1/3}$"> functional (from
J.C.&nbsp;Slater, <I>Quantum Theory of Molecules and Solids, Vol.&nbsp;4: The
  Self-Consistent Field for Molecules and Solids</I> (McGraw-Hill, New
Y