# [molpro-user] About Size consistent problem in O2H+

george george.iitm at gmail.com
Thu Dec 15 17:44:34 CET 2016

```Dear users

I am calculating CBS PES of O2H+ ion. When I calculate a single point
calculation of X-state keeping the distance between OH+ fragment and O-atom
at 50 Ang at CAS/cc-pVQZ level, I get the following energy at CAS level
E_cas = -149.8371634 hartrees.

Now, I do the individual calculation at the same level of the OH+ ion and
O-atom seperately and I get E_cas(OH+) = -75.02897195 hartrees and E_cas(O)
= -74.80987715 hartrees. When I sum, I get E_cas(OH+ and O) = -149.83884910
hartrees. I find that the summed energy and energy of the O2H+ ion
calculated at 50 Ang differ by 0.0016857 hartrees which is sizable
according to my opinion.

My question is that if there is any way out to reduce this difference to
almost zero hartrees (i.e to say about 0.000001 hartrees)

I write below input file I used for each of the above mentioned calculation
for the users to find out the possible mistakes in them if any

I will be happy to receive any comments from the experienced users to this
issue.

Input file for O2H+ ion at 50 Ang
-----------------------------------------------
***,o2hp
print,orbitals,civector

!file,1,
o2hp_ci_cs_2_1_titan.int
file,2,b.wfu

!symmetry,x

rcm=[1.258030346,0.9,1,1.1,1.15,1.2,1.25,1.3,1.35,1.4,1.5,1.6,1.7,1.8,1.9,2.0,2.05,2.1,2.2,2.3,2.4,2.6,2.8,\

3,3.2,3.4,3.6,3.8,4,4.5,5,6,8,10,15,20,30,50] ANG

roh=1.008682076 ANG
theta=30 DEGREE

basis=cc-pVQZ

do i=1,#rcm

ro=rcm(i)

symmetry,x
geometry={
!geometry
specification, using z-matrix
3
O2HP
O          0         0              -(1/17)*roh
H          0         0              (16/17)*roh
O          0     ro*sin(theta)     ro*cos(theta)
}

{multi;config;wf,16,2,2;state,5;dm}
emulti_gs(i)=energy(1)
emulti_1xs(i)=energy(2)
emulti_2xs(i)=energy(3)
emulti_3xs(i)=energy(4)
emulti_4xs(i)=energy(5)
{ci;option,maxiti=5000;wf,16,2,2;state,5}
eci_gs(i)=energy(1)
eci_1xs(i)=energy(2)
eci_2xs(i)=energy(3)
eci_3xs(i)=energy(4)
eci_4xs(i)=energy(5)

table,rcm,emulti_gs,emulti_1xs,emulti_2xs,emulti_3xs,emulti_4xs
Title,Results for O2H+
table,rcm,eci_gs,eci_1xs,eci_2xs,eci_3xs,eci_4xs

end do

{pop;individual;density,2140.2,charge,state=1.2}
{pop;individual;density,2140.2,charge,state=2.2}
{pop;individual;density,2140.2,charge,state=3.2}
{pop;individual;density,2140.2,charge,state=4.2}
{pop;individual;density,2140.2,charge,state=5.2}

Input file for OH+ fragment
-------------------------------------------
***,o2h+
print,orbitals,civector
file,1,oh+_ci_c2v_4_1_mar5.int
file,2,oh+_ci_c2v_4_1_mar5.wfu

!rcm=[1.0275782448,0.5,0.55,0.6,0.65,0.7,0.75,0.8,0.85,0.9,0.925,0.95,0.975,
1,1.025,1.05,1.075,1.1,1.15,1.2,1.4,1.6,\
!     1.8,2,2.5,3,3.5,4,4.5,5,6,8,10,12,14,16,18,20] ANG
rcm=[1.008682076] ANG

geometry={
!geometry
specification, using z-matrix
o
h o roh
}

basis=cc-pVQZ

do i=1,#rcm

roh=rcm(i)

{multi;config;wf,8,4,2;dm}
emulti_gs(i)=energy(1)
ci
eci_gs(i)=energy(1)
eci_gs_david(i)=energd(1)

end do

table,rcm,emulti_gs,eci_gs,eci_gs_david
Title,Results for OH+ dissociation 3Sig- state

{pop;individual;density,2140.2,charge,state=1.4}

Input file for O-atom
----------------------------------
***,o
print,orbitals,civector

geometry={
!geometry
specification, using z-matrix
o
}

basis=cc-pVQZ

{multi;wf,8,4,2;dm}
ci
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