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<TITLE>24. Hessians</TITLE>
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HREF="node27.html">25. Vibrational frequencies</A>
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HREF="node25.html">23. Hybrid Calculations with</A>
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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="tex2html1485"
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HREF="node26.html#SECTION002610000000000000000">24.1 Hessian Module Input</A>
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<UL>
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<LI><A NAME="tex2html1486"
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HREF="node26.html#SECTION002611000000000000000">24.1.1 Defining the wavefunction threshold</A>
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<LI><A NAME="tex2html1487"
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HREF="node26.html#SECTION002612000000000000000">24.1.2 Profile</A>
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<LI><A NAME="tex2html1488"
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HREF="node26.html#SECTION002613000000000000000">24.1.3 Print Control</A>
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<H1><A NAME="SECTION002600000000000000000">
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24. Hessians</A>
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</H1>
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<A NAME="sec:hess"></A>
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<P>
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This section relates to the computation of analytic hessians which
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are available for open and closed shell SCF, except ROHF and for closed shell
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DFT. Analytic hessians are not currently available for SCF or DFT
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calculations relativistic all-electron methodologies or for charge fitting with DFT. The current
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algorithm is fully in-core and does not use symmetry. This will be
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changed in the next release.
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<P>
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There is no required input for the Hessian module. This module only
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impacts the hessian calculation. For options for calculating the
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frequencies, please see Section <A HREF="node27.html#sec:vib">25</A>, the Vibrational module.
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<P>
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<H1><A NAME="SECTION002610000000000000000">
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24.1 Hessian Module Input</A>
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</H1>
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<P>
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All input for the Hessian Module is optional since the default
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definitions are usually correct for most purposes.
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The generic module input begins with <code>hessian</code>
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and has the form:
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<PRE>
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hessian
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thresh <real tol default 1d-6>
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print ...
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profile
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end
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</PRE>
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<P>
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<H2><A NAME="SECTION002611000000000000000">
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24.1.1 Defining the wavefunction threshold</A>
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</H2>
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You may modify the default threshold for the wavefunction. This keyword
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is identical to THRESH in the SCF, Section <A HREF="node12.html#sec:thresh">10.7</A>, and the
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CONVERGENCE gradient in the DFT, Section <A HREF="node13.html#sec:dftconv">11.7</A>. The usual
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defaults for the convergence of the wavefunction for single point and
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gradient calculations is generally not tight enough for analytic hessians.
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Therefore, the hessian, by default, tightens these up to 1d-6 and runs
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an additional energy point if needed. If,
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during an analytic hessian calculation, you encounter an error:
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<PRE>
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cphf_solve:the available MOs do not satisfy the SCF equations
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</PRE>
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the convergence criteria of the wavefunction generally needs to be
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tightened.
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<P>
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<H2><A NAME="SECTION002612000000000000000">
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24.1.2 Profile</A>
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</H2>
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The PROFILE keyword provides additional information concerning the
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computation times of
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different sections of the hessian code. Summary information is
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given about the maximum, minimum and average times that a particular
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section of the code took to complete. This is normally only useful
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for developers.
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<P>
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<H2><A NAME="SECTION002613000000000000000">
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24.1.3 Print Control</A>
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</H2>
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Known controllable print options are:
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<P>
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<BR><P></P>
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<DIV ALIGN="CENTER"><A NAME="6673"></A>
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<TABLE>
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<CAPTION><STRONG>Table 24.1:</STRONG>
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Hessian Print Control Specifications</CAPTION>
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<TR><TD>
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<DIV ALIGN="CENTER">
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<TABLE CELLPADDING=3 ALIGN="CENTER">
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<TR><TD ALIGN="LEFT"><B>Name</B></TD>
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<TD ALIGN="CENTER"><B>Print Level</B></TD>
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<TD ALIGN="CENTER"><B>Description</B></TD>
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</TR>
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<TR><TD ALIGN="LEFT">``hess_follow''</TD>
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<TD ALIGN="CENTER">high</TD>
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<TD ALIGN="CENTER">more information about where the calculation is</TD>
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</TR>
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<TR><TD ALIGN="LEFT">``cphf_cont''</TD>
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<TD ALIGN="CENTER">debug</TD>
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<TD ALIGN="CENTER">detailed CPHF information</TD>
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</TR>
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<TR><TD ALIGN="LEFT">``nucdd_cont''</TD>
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<TD ALIGN="CENTER">debug</TD>
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<TD ALIGN="CENTER">detailed nuclear contribution information</TD>
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</TR>
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<TR><TD ALIGN="LEFT">``onedd_cont''</TD>
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<TD ALIGN="CENTER">debug</TD>
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<TD ALIGN="CENTER">detailed one electron contribution information</TD>
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</TR>
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<TR><TD ALIGN="LEFT">``twodd_cont''</TD>
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<TD ALIGN="CENTER">debug</TD>
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<TD ALIGN="CENTER">detailed two electron contribution information</TD>
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</TR>
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<TR><TD ALIGN="LEFT">``fock_xc''</TD>
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<TD ALIGN="CENTER">debug</TD>
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<TD ALIGN="CENTER">detailed XC information during the fock builds</TD>
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</TR>
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</TABLE>
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</DIV>
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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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HREF="node25.html">23. Hybrid Calculations with</A>
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<ADDRESS>
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Edoardo Apra
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2004-05-25
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