Re: W:MCSCF GAMESS-US input?

From: "Gustavo, Alberto, Mercier" <gamercier -()-
 yahoo.com>
 <<<<<<<<<<<<<
 ..................
 1) Set RUNTYP=MCSCF in CONTRL
 2) Set GUESS GUESS=MOREAD NORB=426  to read all the orbitals, alpha and beta
 using  the VEC namelist
 3) Set DET NCORE=87 NACT=14 NELS=9 GROUP=C2V ISTSYM=1 NSTATE=1
 ..................
 Question 1)
 It is not clear to me how the program will pick up the correct number of alpha
 and beta orbitals
 with the above input. It seems that something is
 missing to force the program to split the active orbitals into 10 alpha and 4i
 beta orbitals. (This may be easier with the 5 spherical d orbitals. i
 In this case NACT=13. By making Sz=5/2 this will pick 5 alpha orbitals i
 for the active space and split the rest evenly between alphas and betas.)
 Does any one have any suggestions or can shed light on this problem?
 ................
 >>>>>>>>>>>>>>>>>>
    You input specifies 87 core, 14 active orbitals and 9
 active electrons. With 5 odd electrons there will be
 2 doubly occupied and 5 singly occupied and 7 vacant orbitals
 in the MCSCF active space. I never used UHF orbitals as starting
 guess for MCSCF myself. The way I understand how Gamess would handle
 your input is that it will pick up the top 87+14=101 orbitals from VEC.
 The first 87 will be the core MOs, the following 14 correspond to the
 sequence of doubly and singly occupied and virtual orbitals implied
 in you $DET card.
   Your VEC card generated from a UHF run begins with a set of
 UHF alpha MOs followed by the same number of beta MOs. The number
 should equal the number of cartesian basis functions. I suppose
 it is the same number as NORB(426). I presume your MCSCF run will
 pick up the 88--89th UHF alpha MOs as the first two doubly occupied
 MOs, the 90--94th alpha MOs as the 5 singly occupied MOs and
 the following 7 vacant alpha UHF MOs as the virtual MOs
 in the active wavefunction space. The entire set of beta UHF-MOs
 in VEC will be ignored as far as I can understand.
    Idealy the final result of a MCSCF run is independent of the
 starting guess orbitals. In reality the guess MOs should
 be "sensible". So it is prudent to use a set
 of guess MOs that emulate the occupancy of the final MCSCF orbitals closely.
 You may avoid the confusion over the splitting between alpha and
 beta electrons in the MCSCF active space by using ROHF instead of UHF.
   A better method of generating initial guess I would recommend
 is to use UHF-natural orbitals.
 	In your UHF input file specify UHFNOS=.TRUE. in the $SCF card.
 You will obtain a set of unrestricted natural orbitals in a VEC card
 in the punch file. Note that the occupancies  of the UNOs are also
 indicated. Use the UNOs instead of the UHF-MOs for your MCSCF runs.
 You can base your selection of active space on the occupancies of the
 UNOs. You will find that the SOMOs will have a  fractional occupancy near unity.
 The occupancies of the virtual MOs following the SOMO diminish gradually.
 The highest doubly occpied MO and
 the few preceeding MOs will have an occupancy smaller than 2.
 UNOs falling into the occupancy range of 0.02--1.98
 will make good starting guess for your MCSCF run.
 Wai-To Chan