# [molpro-user] Discrepancy in energy values

Bhargava Anusuri bhargava.anusuri at gmail.com
Sun Jan 8 07:20:50 CET 2017

```Dear users,
I am computing potential energy surface of CCH+ using
Molpro. I have observed that there is a difference in energy values for the
same geometry when it was computed in a loop and when it is computed
separately as a single point.

r(C-H) = 2.4 a.u , r(C-C) = 21.9 a.u, C-C-H angle = 179 degree :
-75.74572157 hartree (Single point)

-75.78211095 hartree (in a loop)

My input for loop is

***,CCH+
memory,70,m
gthresh,energy=0.32d-6

r=1.0d0
rc=2.4d0
theta = 179 deg

geometry={
C1;
C2,C1,r;
H,C2,rc,C1,theta}

basis=aug-cc-pVQZ

do i=1,56

{hf;wf,12,2,2}

{multi;
maxiter,40;
pspace,0.3;
wf,12,2,2}

{ci;
option,maxit=90

option,maxiti=9000;
!option,nstati=2;
option,cluster=2;

wf,12,2,2}

e(i)=energy
ed(i)=energd2

if(i.lt.3) then
r=r+0.2d0
elseif(i.ge.3).and.(i.lt.24) then
r=r+0.1d0
elseif(i.ge.24).and.(i.lt.36) then
r=r+0.2d0
elseif(i.ge.36).and.(i.lt.44) then
r=r+0.5d0
else
r=r+1.0d0
endif

{table,sr,capr,e,ed
save,179d.dat,new
}

enddo

Is there something I am doing wrong? Any help is greatly appreciated.