[molpro-user] help regarding MRCI calculations

[rama chandran]

Dear friends,
I am very new to molpro suite of programs.

I calculated the energy of a linear HeHH+ 3 electron
system reported in a paper.
Pls. see the input below.


***,HeH2plus
 Memory,100,M
 geometry={H;
 H1,H,r1;
 He,H,r2,H1,a1}
  r1=2.075338
  r2=1.931059
  a1= 180.0
 basis=v5Z
{HF
occ,2,0,0,0
wf,charge=1,symmetry=1,spin=1
}
casscf
mrci



According to that paper, the calculations have done
using CASSCF method and recovered the dynamic
correlation energy by the interanally contracted MRCI
method.  The basis set used were cc-pV5Z of Dunning
(8s4p3d2f1g) contracted to [5s4p3d2f1g].

As you see in the input file, I tried the same method
and basis set for the geometry specified in
literature.
However, I am getting a slightly different energy.
For example, the energy reported is -3.51889301  where
as I got the value of -3.518185866
Although the difference is very small, I afraid
something is wrong in the calculations (Input file).
I couldn't reproduce the result for other geometries
also.

He is approaching H2^+ in a linear fashion.
So as per molpro symmetry constraints it can have C2v
symmetry.
As it is a 3 electron system now, it would have filled
sigma-g and sigma-u orbitals.
So the occupied levels as per the notation I guess,
2,0,0,0.
I doubt whether I made any mistake in this step or
not.

I am a novice in these calculations and from manual I
got only these much.

(2)   If  He is approaching by making an angle <180  
it will have Cs symmetry.
So the irreducible representation will be A' and A''
So what should be the configuration? 

Can anyone help me?

Thanks in advance.



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