RASSCF and a very confusing result

Posted by pawel wielgus on May 02, 2006 at 17:59:17:

Dear MOLCAS Users,

I'm trying to simulate MRCI for C2 dimer using RASSCF code (the reason for this is pretty good but this is a different story). First of all I'm doing CAS with 1sig(g) and 1sig(u) as inactive, and then RASSCF code is run for the second time with CIONly and ras3 space covering all of the orbitals available and max number of occupation equal 2 (please see the attached input for a better feeling). The problem which I see is that this second RAS calculation "converges" in an unusual way, just with one step, which should be, roughly speaking, impossible:
Iter CI SX CI RASSCF Energy max BLB max BLB max ROT Level Ln srch Step QN Time(min)
iter iter root energy change element value param shift minimum type update CPU
1 1 0 1 -75.76013969 .00E+00 1 3 4 -.76E-02 .00E+00 .00 .00 SX NO 1.40

************************************************************************************************************************

Am I right that something is wrong with this?
Could anyone try to run the attached input file or explain me what's happening ?

I'd really appreciate your help,

Pawel Wielgus

P.S. This is not my very original input since I'm working with more than 50 active orbitals and to calculate this I had to recompile Molcas (BTW 6.4 patchlevel 099) with increased mxact in $MOLCAS/src/Include/Molcas.fh. But I also checked it with the original code and decreased Ras3 space, so I'm giving you the second one. I know that right now it's not very 'meaningful', but for testing purposes it's enough I believe...

INPUT
&SEWARD &END
Title
C2 Dimer R=1.2520 BS=cc-pVTZ
Symmetry
X Y Z
Basis set
C.CC-PVTZ....
C 0.0 0.0 0.626000 Angstrom
End of basis
End of input

&SCF &END
Title
C2 Dimer R=1.2520 BS=cc-pVTZ
Rhf
*Aufbau
* 6 2
Occupied
2 1 1 0 2 0 0 0
Iterations
100
*Lumorb
*Ivo
End of input

&RASSCF &END
Title
C2 Dimer R=1.2520 BS=cc-pVTZ
Symmetry
1
Spin
1
NActEl
8 0 0
Inactive
1 0 0 0 1 0 0 0
Ras2
2 1 1 0 2 1 1 0
LumOrb
End of input

&RASSCF &END
Title
C2 Dimer R=1.2520 BS=cc-pVTZ
Symmetry
1
Spin
1
NActEl
8 0 2
Frozen
1 0 0 0 1 0 0 0
Ras2
2 1 1 0 2 1 1 0
Ras3
8 5 5 1 8 5 5 1
CIOnly
LumOrb
End of input

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Comments:
: Dear MOLCAS Users, : I'm trying to simulate MRCI for C2 dimer using RASSCF code (the reason for this is pretty good but this is a different story). First of all I'm doing CAS with 1sig(g) and 1sig(u) as inactive, and then RASSCF code is run for the second time with CIONly and ras3 space covering all of the orbitals available and max number of occupation equal 2 (please see the attached input for a better feeling). The problem which I see is that this second RAS calculation "converges" in an unusual way, just with one step, which should be, roughly speaking, impossible: : Iter CI SX CI RASSCF Energy max BLB max BLB max ROT Level Ln srch Step QN Time(min) : iter iter root energy change element value param shift minimum type update CPU : 1 1 0 1 -75.76013969 .00E+00 1 3 4 -.76E-02 .00E+00 .00 .00 SX NO 1.40 : ************************************************************************************************************************ : : Am I right that something is wrong with this? : Could anyone try to run the attached input file or explain me what's happening ? : I'd really appreciate your help, : Pawel Wielgus : P.S. This is not my very original input since I'm working with more than 50 active orbitals and to calculate this I had to recompile Molcas (BTW 6.4 patchlevel 099) with increased mxact in $MOLCAS/src/Include/Molcas.fh. But I also checked it with the original code and decreased Ras3 space, so I'm giving you the second one. I know that right now it's not very 'meaningful', but for testing purposes it's enough I believe... : INPUT : &SEWARD &END : Title : C2 Dimer R=1.2520 BS=cc-pVTZ : Symmetry : X Y Z : Basis set : C.CC-PVTZ.... : C 0.0 0.0 0.626000 Angstrom : End of basis : End of input : &SCF &END : Title : C2 Dimer R=1.2520 BS=cc-pVTZ : Rhf : *Aufbau : * 6 2 : Occupied : 2 1 1 0 2 0 0 0 : Iterations : 100 : *Lumorb : *Ivo : End of input : : &RASSCF &END : Title : C2 Dimer R=1.2520 BS=cc-pVTZ : Symmetry : 1 : Spin : 1 : NActEl : 8 0 0 : Inactive : 1 0 0 0 1 0 0 0 : Ras2 : 2 1 1 0 2 1 1 0 : LumOrb : End of input : : &RASSCF &END : Title : C2 Dimer R=1.2520 BS=cc-pVTZ : Symmetry : 1 : Spin : 1 : NActEl : 8 0 2 : Frozen : 1 0 0 0 1 0 0 0 : Ras2 : 2 1 1 0 2 1 1 0 : Ras3 : 8 5 5 1 8 5 5 1 : CIOnly : LumOrb : End of input

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