# [molpro-user] Convergence issues in SCF calculations

Sunil sunil.phys at gmail.com
Sun Mar 15 07:23:39 GMT 2009

```Dear Users,

I have been trying to calculate the potential energy surface of
three-times-ionized CO2 molecule using the program given below. The program
does not converge even in the HF level when the variable "i" is above 10 or
so. Can you please help me in deciding what modification I can do to the
program so as to get convergence? Thanks in advance.

-sunil
---------------------------------------------------------------------------------------

*** CO2 PE curve                        ! Title: PE Curve for CO2
print basis,orbitals,civector
geomtyp=zmat
geometry
ang
C
O1 C rco1(k)
O2 C rco2(k) O1 oco
end

r1(1) = 0.7500000 Ang
r2(1) = 0.7500001 Ang
dr = 0.05 Ang

do i = 1,50
r1(i+1) = r1(i) + dr
r2(i+1) = r2(i) + dr
enddo

oco = 180 Degree

basis = 6-311G++(2DF,2PD)               ! Basis set specification
k = 0
do i = 1,#r1
do j = 1,i
k=k+1
rco1(k) = r1(i)
rco2(k) = r2(j)

hf;
occ 7 2 1 0
wf 19 2 1
open 2.2
enhf(k)=energy

enddo
enddo

table rco1,rco2,enhf