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2.3. GENERATING MO START VECTORS
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shell can be specified at a time. Watch the headline of the menu, which
tells you the number of electrons assigned to MOs.
Description of Commands
s list
This command gives you a listing of all MOs and their energies as obtained from the extended Hückel calculation. For NH3 in C3v and TZVP
you get, e.g.:
ORBITAL SYMMETRY ENERGY
SHELL
CUMULATED CL.SHL OCC.
(SHELL)
TYPE
DEGENERACY SHELL DEG. PER ORBITAL
1
1a1
-15.63244
2
2
0.0000
2
2a1
-0.99808
2
4
0.0000
3
1e
-0.64406
4
8
0.0000
4
3a1
-0.57085
2
10
0.0000
5
2e
0.30375
4
14
0.0000
6
4a1
0.87046
2
16
0.0000
TO CONTINUE, ENTER <return>
OP.SHL OCC.
PER ORBITAL
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
p index
This allows you to get the linear combination of basis functions which
form the MO-index. Note that this refers not to the basis set you specified, but to the extended Hückel basis. index must be a single index,
not an index list.
c list
This command allows you to specify closed shells. Their occupation will
be 2 per MO, the total occupation the shell degeneracy which you can
obtain by using command s. list is a list of shell indices like 1-13 or
1,3-5,7.
o index
This command allows you to specify open shells. index must be a single
shell index, not an index list. You will then be asked for the number of
electrons per MO which shall be contained in this shell. For example,
for a fluorine atom you should choose o n (where n is the index of
the p-shell) and an occupation of 5/3 per MO. You may enter the
occupation numbers as simple integers or as integer fractions, e.g. 1 for
the s-occupation in sodium, 5/3 for the p-occupation in fluorine.
v list
With this command you can remove an orbital occupation, if you specified a wrong one. list is again a list of shell indices in usual syntax.
&
This command has a different meaning in this menu than in the rest of
Define. Here it will repeat the extended Hückel calculation (perhaps
you want to change some Hückel parameters for the next one).
*
* will not bring you back to the occupation numbers menu, but will
terminate the whole occupation number and start vector section and
will bring you to the last main menu, which is described in Section 2.4.
If you want to leave this menu without assigning all electrons in your
molecule to shells, Define will issue a warning and suggest to continue