[molpro-user] HOW TO 'MERGE' TO GENERATE ORBITALS FROM FRAGMENTS
Dr. Seth Olsen
s.olsen1 at uq.edu.au
Fri Mar 24 07:24:04 GMT 2006
This communique is connected to my previous communique entitled
'Overriding geometry (and basis) reordering in molpro?' but is not meant
to conclude that thread. I have figured out how to perform the
immediate task I had before me at that time - i.e. generating an orbital
set for benzene dimer using orbitals taken from calculations on the
individual fragments using the MERGE facility. Unfortunately, MERGE is
not terribly well documented on the molpro website and the examples
presented are not terribly useful. This is because in these examples,
the elements represented by each fragment don't overlap. This means
that they will not run into MolPro's (somewhat frustrating) habit of
reordering the atoms and the basis set into blocks of a common element.
This in turn means that the composite orbitals are easily generated via
the MOVE command, and offsets, etc. are not needed. However, if the
atoms are rearranged, generating the appropriate MERGE deck quickly
becomes more complicated. Of course, for the case of benzene dimer,
where the fragments are identical, one would run into this problem.
In order to provide a better example of how MERGE should be used when
fragments share common elements, I am posting a gzipped version of my
calculation on benzene dimer to the list. The input deck is echoed in
the output file. The aim of the calculation was to create an orbital
set for benzene excimer that did not explicitly make use of symmetry,
but where the six pi orbitals of each fragment were coupled high-spin in
an ROHF calculation. These orbitals are then interleaved to create the
dimer orbitals. No final ROHF-SCF is performed on the dimer, but the
final orbitals are output in molden and ascii format. Note - unless you
tweak the molden file it will not display properly using programs like
MOLEKEL or GABEDIT. In order to make these work, you have to reorder
the atoms to the element-block format found in molpro (i.e. all C's
followed by all H's). Alternatively, one could reorder the basis and
all the orbitals, but this is a little more of a bother.
Enjoy, and I hope it is of use to someone.
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