# [molpro-user] Problem with Catastrophic failure in diagonalization(hsdel)

Fri Dec 4 10:31:43 CET 2015

```Dear Molpro-users,

I tried to calculate the potential energy curves of symmetry4&5 of nitrogen
molecule(all singlet).
And I have used various ways to deal with this problem.
But none of them works.
May I ask you how to solve this problem?

below is my input & output
============================================================
memory,32,M
GEOMETRY = { ang; N1; N2,N1,r(i)}

BASIS = AVTZ

R1=0.6
DO   i=0,136
r(i)= R1+i*0.025

{RHF;wf,14,1,0;occ,3,1,1,0,2,0,0;closed,1,0,0,0,1,0,0}
{CASSCF;occ,3,1,1,0,2,1,1;closed,1,0,0,0,1,0,0;wf,14,5,0}
{mrci,nocheck;OPTION,NSTATI=10;pspace,1.5}
e51(i)=energy(1)

table,r,e51

enddo
table,r,e51

Number of p-space configurations:  12
Internal expansion vectors linearly dependent.
Smallest eigenvalue of S:  0.4766406E-15. Vector removed
Internal expansion vectors linearly dependent.
Smallest eigenvalue of S:  0.1594559E-15. Vector removed
Internal expansion vectors linearly dependent.
Smallest eigenvalue of S: -0.8619501E-15. Vector removed
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

===============================================================

Thank you so much for your help.

Best regards,

Hung-an
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