[molpro-user] How to input singlet Pi state ?(1)

Peter REINHARDT reinh at lct.jussieu.fr
Fri Oct 7 08:45:29 BST 2005

On Fri, Oct 07, 2005 at 11:29:12AM +0800, Chuanlu Yang wrote:
> molpro-user :
> ??Thanks! But I think what you said is not the key points.?? 
> The key problem is how to specify the singlet in molpro ? For Sigma state, singlet means close shell. However, Pi singlet cannot the case. In my impression, molpro usually give triplet when two orbitals are open. Obviously, we must get the two orbitals having opposite spin if we want singlet. In fact, molpro manual say the command ??open?? can specify the ??+?? or ??-?? of spin, but I find it no use.Now, I do not know what to do. 

Dear Changlu,
I think you nearly got it : how do you want to represent a singlet with two open shells with 
one determinant? For the singlet you need Up-Down - Down-Up, so at least two determinants.
Or you do a high-spin calculation for the triplet. 
So try a MCSCF calculation with two references instead of Hartree-Fock.


> Chuanlu Yang ?? yangchuanlu at 263.net 
> 2005-10-7 

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