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HREF="node18.html">16. MP2</A>
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  <B> <A NAME="tex2html1333"
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HREF="node2.html">Contents</A></B>
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<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
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<UL>
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<LI><A NAME="tex2html1336"
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HREF="node19.html#SECTION001910000000000000000">17.1 <TT>ACTIVE</TT> -- Number of active orbitals</A>
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<LI><A NAME="tex2html1337"
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HREF="node19.html#SECTION001920000000000000000">17.2 <TT>ACTELEC</TT> -- Number of active electrons</A>
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<LI><A NAME="tex2html1338"
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HREF="node19.html#SECTION001930000000000000000">17.3 <TT>MULTIPLICITY</TT></A>
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<LI><A NAME="tex2html1339"
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HREF="node19.html#SECTION001940000000000000000">17.4 <TT>SYMMETRY</TT> -- Spatial symmetry of the wavefunction</A>
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<LI><A NAME="tex2html1340"
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HREF="node19.html#SECTION001950000000000000000">17.5 <TT>STATE</TT> -- Symmetry and multiplicity</A>
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<LI><A NAME="tex2html1341"
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HREF="node19.html#SECTION001960000000000000000">17.6 <TT>VECTORS</TT> -- Input/output of MO vectors</A>
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<LI><A NAME="tex2html1342"
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HREF="node19.html#SECTION001970000000000000000">17.7 <TT>HESSIAN</TT> -- Select preconditioner</A>
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<LI><A NAME="tex2html1343"
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HREF="node19.html#SECTION001980000000000000000">17.8 <TT>LEVEL</TT> -- Level shift for convergence</A>
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<LI><A NAME="tex2html1344"
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HREF="node19.html#SECTION001990000000000000000">17.9 <TT>PRINT</TT> and <TT>NOPRINT</TT></A>
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</UL>
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<HR>
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<H1><A NAME="SECTION001900000000000000000">
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17. Multiconfiguration SCF</A>
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</H1>
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<A NAME="sec:mcscf"></A>
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<P>
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The NWChem multiconfiguration SCF (MCSCF) module can currently perform
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complete active space SCF (CASSCF) calculations with at most 20 active
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orbitals and about 500 basis functions. It is planned to extend it to
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handle 1000+ basis functions.
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<P>
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<PRE>
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MCSCF
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STATE <string state>
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ACTIVE <integer nactive>
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ACTELEC <integer nactelec>
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MULTIPLICITY <integer multiplicity>
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[SYMMETRY <integer symmetry default 1>]
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[VECTORS [[input] <string input_file default $file_prefix$.movecs>]
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[swap <integer vec1 vec2> ...] \
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[output <string output_file default input_file>] \
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[lock]
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[HESSIAN (exact||onel)]
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[MAXITER <integer maxiter default 20>]
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[THRESH <real thresh default 1.0e-4>]
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[TOL2E <real tol2e default 1.0e-9>]
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[LEVEL <real shift default 0.1d0>]
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END
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</PRE>
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Note that the <code>ACTIVE</code>, <code>ACTELEC</code>, and <code>MULTIPLICITY</code>
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directives are <EM>required</EM>. The symmetry and multiplicity may
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alternatively be entered using the <code>STATE</code> directive.
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<P>
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<H1><A NAME="SECTION001910000000000000000">
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17.1 <TT>ACTIVE</TT> -- Number of active orbitals</A>
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</H1>
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<P>
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The number of orbitals in the CASSCF active space must be specified
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using the <TT>ACTIVE</TT> directive.
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<P>
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E.g.,
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<PRE>
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active 10
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</PRE>
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<P>
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The input molecular orbitals (see the vectors directive, Sections
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<A HREF="node19.html#sec:mcscfvectors">17.6</A> and <A HREF="node12.html#sec:vectors">10.5</A>) must be arranged in
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order
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<OL>
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<LI>doubly occupied orbitals,
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</LI>
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<LI>active orbitals, and
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</LI>
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<LI>unoccupied orbitals.
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</LI>
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</OL>
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<P>
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<H1><A NAME="SECTION001920000000000000000">
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17.2 <TT>ACTELEC</TT> -- Number of active electrons</A>
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</H1>
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<P>
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The number of electrons in the CASSCF active space must be specified
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using the the <TT>ACTELEC</TT> directive. An error is reported if the
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number of active electrons and the multiplicity are inconsistent.
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<P>
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The number of closed shells is determined by subtracting the number
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of active electrons from the total number of electrons (which in turn
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is derived from the sum of the nuclear charges minus the total system
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charge).
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<P>
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<H1><A NAME="SECTION001930000000000000000">
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17.3 <TT>MULTIPLICITY</TT></A>
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</H1>
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<P>
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The spin multiplicity must be specified and is enforced by projection
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of the determinant wavefunction.
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<P>
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E.g., to obtain a triplet state
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<PRE>
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multiplicity 3
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</PRE>
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<P>
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<H1><A NAME="SECTION001940000000000000000">
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17.4 <TT>SYMMETRY</TT> -- Spatial symmetry of the wavefunction</A>
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</H1>
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<P>
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This species the irreducible representation of the wavefunction as an
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integer in the range 1--8 using the same numbering of representations
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as output by the SCF program. Note that only Abelian point groups are
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supported.
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<P>
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E.g., to specify a <IMG
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WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
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SRC="img142.gif"
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ALT="$B_1$"> state when using the <IMG
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WIDTH="29" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
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SRC="img7.gif"
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ALT="$C_{2v}$"> group
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<PRE>
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symmetry 3
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</PRE>
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<P>
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<H1><A NAME="SECTION001950000000000000000">
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17.5 <TT>STATE</TT> -- Symmetry and multiplicity</A>
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</H1>
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<P>
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The electronic state (spatial symmetry and multiplicity) may
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alternatively be specified using the conventional notation for an
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electronic state, such as <IMG
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WIDTH="30" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
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SRC="img143.gif"
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ALT="$^3B_2$"> for a triplet state of <IMG
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WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
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SRC="img144.gif"
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ALT="$B_2$">
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symmetry. This would be accomplished with the input
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<PRE>
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state 3b2
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</PRE>
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which is equivalent to
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<PRE>
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symmetry 4
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multiplicity 3
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</PRE>
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<P>
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<H1><A NAME="SECTION001960000000000000000"></A>
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<A NAME="sec:mcscfvectors"></A>
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<BR>
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17.6 <TT>VECTORS</TT> -- Input/output of MO vectors
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</H1>
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<P>
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Calculations are best started from RHF/ROHF molecular orbitals (see
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Section <A HREF="node12.html#sec:scf">10</A>), and by default vectors are taken from the
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previous MCSCF or SCF calculation. To specify another input file use
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the <code>VECTORS</code> directive. Vectors are by default output to the
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input file, and may be redirected using the <code>output</code> keyword.
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The <code>swap</code> keyword of the <code>VECTORS</code> directive may be
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used to reorder orbitals to obtain the correct active space.
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See Section <A HREF="node12.html#sec:vectors">10.5</A> for an example.
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<P>
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The <code>LOCK</code> keyword allows the user to specify that the ordering
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of orbitals will be locked to that of the initial vectors, insofar as
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possible. The default is to order by ascending orbital energies within
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each orbital space. One application where locking might be desirable
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is a calculation where it is necessary to preserve the ordering of a
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previous geometry, despite flipping of the orbital energies. For such
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a case, the <code>LOCK</code> directive can be used to prevent the SCF
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calculation from changing the ordering, even if the orbital energies
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change.
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<P>
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Output orbitals of a converged MCSCF calculation are canonicalized as
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follows:
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<UL>
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<LI>Doubly occupied and unoccupied orbitals diagonalize the
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corresponding blocks of an effective Fock operator. Note that in
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the case of degenerate orbital energies this does not fully
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determine the orbtials.
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</LI>
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<LI>Active-space orbitals are chosen as natural orbitals by
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diagonalization of the active space 1-particle density matrix.
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Note that in the case of degenerate occupations that this
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does not fully determine the orbitals.
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</LI>
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</UL>
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<P>
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<H1><A NAME="SECTION001970000000000000000"></A>
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<A NAME="sec:mcscfhessian"></A>
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<BR>
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17.7 <TT>HESSIAN</TT> -- Select preconditioner
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</H1>
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<P>
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The MCSCF will use a one-electron approximation to the orbital-orbital
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Hessian until some degree of convergence is obtained, whereupon it
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will attempt to use the exact orbital-orbital Hessian which makes the
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micro iterations more expensive but potentially reduces the total
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number of macro iterations. Either choice may be forced throughout
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the calculation by specifying the appropriate keyword on the
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<code>HESSIAN</code> directive.
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<P>
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E.g., to specify the one-electron approximation throughout
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<PRE>
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hessian onel
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</PRE>
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<P>
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<H1><A NAME="SECTION001980000000000000000">
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17.8 <TT>LEVEL</TT> -- Level shift for convergence</A>
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</H1>
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<P>
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The Hessian (Section <A HREF="node19.html#sec:mcscfhessian">17.7</A>) used in the MCSCF
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optimization is by default level shifted by 0.1 until the orbital
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gradient norm falls below 0.01, at which point the level shift is
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reduced to zero. The initial value of <IMG
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WIDTH="24" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img145.gif"
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ALT="$0.1$"> may be changed using
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the <code>LEVEL</code> directive. Increasing the level shift may make
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convergence more stable in some instances.
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<P>
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E.g., to set the initial level shift to 0.5
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<PRE>
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level 0.5
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</PRE>
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<P>
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<H1><A NAME="SECTION001990000000000000000">
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17.9 <TT>PRINT</TT> and <TT>NOPRINT</TT></A>
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</H1>
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<P>
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Specific output items can be selectively enabled or disabled using the
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<code>print</code> control mechanism (<A HREF="node7.html#sec:printcontrol">5.6</A>) with the
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available print options listed in table(<A HREF="node19.html#MCSCF_print_options">17.9</A>).
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<P>
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<BR><P></P>
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<DIV ALIGN="CENTER"><A NAME="5509"></A>
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<TABLE>
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<CAPTION><STRONG>Table 17.1:</STRONG>
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MCSCF Print Options</CAPTION>
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<TR><TD>
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<P>
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<A NAME="MCSCF_print_options"></A>
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<P>
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<P>
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<BR>
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<BR>
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<TABLE CELLPADDING=3 BORDER="1">
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<TR><TD ALIGN="LEFT">Option</TD>
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<TD ALIGN="RIGHT">Class</TD>
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<TD ALIGN="LEFT">Synopsis</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>ci energy</code></TD>
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<TD ALIGN="RIGHT">default</TD>
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<TD ALIGN="LEFT">CI energy eigenvalue</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>fock energy</code></TD>
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<TD ALIGN="RIGHT">default</TD>
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<TD ALIGN="LEFT">Energy derived from Fock matrices</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>gradient norm</code></TD>
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<TD ALIGN="RIGHT">default</TD>
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<TD ALIGN="LEFT">Gradient norm</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>movecs</code></TD>
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<TD ALIGN="RIGHT">default</TD>
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<TD ALIGN="LEFT">Converged occupied MO vectors</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>trace energy</code></TD>
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<TD ALIGN="RIGHT">high</TD>
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<TD ALIGN="LEFT">Trace Energy</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>converge info</code></TD>
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<TD ALIGN="RIGHT">high</TD>
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<TD ALIGN="LEFT">Convergence data and monitoring</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>precondition</code></TD>
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<TD ALIGN="RIGHT">high</TD>
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<TD ALIGN="LEFT">Orbital preconditioner iterations</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>microci</code></TD>
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<TD ALIGN="RIGHT">high</TD>
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<TD ALIGN="LEFT">CI iterations in line search</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>canonical</code></TD>
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<TD ALIGN="RIGHT">high</TD>
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<TD ALIGN="LEFT">Canonicalization information</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>new movecs</code></TD>
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<TD ALIGN="RIGHT">debug</TD>
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<TD ALIGN="LEFT">MO vectors at each macro-iteration</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>ci guess</code></TD>
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<TD ALIGN="RIGHT">debug</TD>
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<TD ALIGN="LEFT">Initial guess CI vector</TD>
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</TR>
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<TR><TD ALIGN="LEFT"><code>density matrix</code></TD>
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<TD ALIGN="RIGHT">debug</TD>
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<TD ALIGN="LEFT">One- and Two-particle density matrices</TD>
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</TR>
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</TABLE>
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<P>
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<P>
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</TD></TR>
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</TABLE>
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</DIV><P></P>
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<BR>
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<ADDRESS>
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Edoardo Apra
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2004-05-25
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