Catastrophic failure in diagonalization(hsdel)???

Yann Tambouret yannpaul at
Fri Mar 19 17:16:00 GMT 2004

Dear Molpro-users,

I'm trying to calculated the potential energy surfaces of O2 ground and 
first few excited states. I run Multi, Ci (Natorb), and CI (several 
states, lowest lying roots). For certain bond lengths, this final 
program execution returns an error:

Catastrophic failure in diagonalization(hsdel)
The expansion set has become singular
This difficulty can arise for many reasons
Sometimes it helps to redefine P space
Otherwise, try increasing or decreasing reference space or nstati

Can anyone explain to me why this happens?

If it would help, please email me for the full input/output files:
yannpaul at


Yann Tambouret

(question 1)

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