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Excited State, UHF
Only the ground state of a given multiplicity can be
calculated using UHF.
Odd-Electron Systems
Often, anions, cations, or radicals are odd-electron
systems. Normally, the ground states and excited
state configuration can be doublet, quartet or
sextet.
Ground State, RHF
Doublet ground state: This is the most common
configuration. No additional keywords are
necessary.
Quartet: Use the following keyword combination:
QUARTET OPEN(3,3)
Sextet ground state: Use the following keyword
combination: SEXTET OPEN(5,5)
Ground State, UHF
For UHF computations all unpaired electrons are
forced to be spin up (alpha).
Doublet ground state: This is the most common
configuration for a odd electron molecule. No
additional keywords are necessary.
UHF will yield energies different from those
obtained by the RHF method.
Quartet and Sextet ground state: Use the keyword
QUARTET or SEXTET.
Excited State, RHF
First Excited State: The first excited state is actually
the second lowest state (the root=2) for a given
spin system (Doublet, Quartet, Sextet). To request
the first excited state use the following sets of
keywords.
First excited doublet: ROOT=2 DOUBLET C.I.=n,
where n=2 is the simplest case.
First excited quartet: ROOT=2 QUARTET C.I.=n,
where n=4 is the simplest case.
First excited sextet: ROOT=2 SEXTET C.I.=n,
where n=5 is the simplest case.
Second Excited State: The second excited state is
actually the third lowest state (the root=3) for a
given system (Singlet, Triplet, Quintet). To request
the second excited state use the following set of
keywords:
Second excited doublet: ROOT=3 DOUBLET C.I.=n,
where n=3 is the simplest case.
Second excited quartet: ROOT=3 QUARTET C.I.=n,
where n=4 is the simplest case.
Second excited sextet: ROOT=3 SEXTET C.I.=n,
where n=5 is the simplest case.
NOTE: If you get an error indicating the active space is not
spanned, use C.I.> n for the simplest case to increase the
number of orbitals available in the active space. To see the
states used in a C.I. calculation, type MECI as an
additional keyword. The information is printed at the bottom
of the *.out file.
Excited State, UHF
Only the ground state of a given multiplicity can be
calculated using UHF.
Sparkles
Sparkles are used to represent pure ionic charges.
They are roughly equivalent to the following
chemical entities:
Chemical
symbol
Equivalent to...
+ tetramethyl ammonium, potassium
or cesium cation + electron
ChemOffice 2005/Chem3D MOPAC Computations • 171
Specifying the Electronic Configuration