# [molpro-user] MRCI symmetry breaking

Jacky LIEVIN jlievin at ulb.ac.be
Fri Mar 25 10:26:23 GMT 2011

```Dear Toru,

The additional thresh directive actually eliminates the jump at 90.06, but it still occurs at 90.0:

ANGLE       ECASSCF        EMRCI          EMRCIDAV
90.00   -39.61901934   -39.71401806   -39.71754590
90.02   -39.61901934   -39.71401906   -39.71754708
90.04   -39.61901933   -39.71401905   -39.71754707
90.06   -39.61901932   -39.71401903   -39.71754705
90.08   -39.61901930   -39.71401900   -39.71754702
90.10   -39.61901928   -39.71401897   -39.71754699

Any other suggestion?
According to your comment, I've now calculated all points with Cs symmetry, using the following input:

*** CH3 fondamental
gthresh,energy=1.d-8,step=1.d-5
gprint,orbitals
basis=vdz
rx=1.0 ang
r=1.09503    ang
hx=90.0
dhh=0.02
hh=hx
d=120
symmetry,y
geometry={C;H2 C r;X1 C rx H2 hh;H3 C r X1 hh H2 d;H4 C r X1 hh H2 -d}
{hf
wf,9,1,1}
hh=hh-dhh
do i=1,6
hh=hh+dhh
symmetry,y
geometry={C;H2 C r;X1 C rx H2 hh;H3 C r X1 hh H2 d;H4 C r X1 hh H2 -d}
{multi
closed,1
wf,9,1,1
print,civector}
angle(i)=hh
ecasscf(i)=energy(1)
{ci
wf,9,1,1
thresh,THRDLP=1.0d-10,THRNRM=1.0d-10}
emrcidav(i)=energd(1)
emrci(i)=energy(1)
enddo
table,angle,ecasscf,emrci,emrcidav
---

Le 25 mars 2011 à 09:50, Toru Shiozaki a écrit :

> Dear Jacky,
> the jump in 90.06 is related to the pair elimination when orthogonal pair functions are generated.
> Could you try the tighter thresholds for thrdlp and thrnrm as follows (or tighter value if you want):
> {mrci; thresh,THRDLP=1.0d-10,THRNRM=1.0d-10}
>
> In addition, it is not a good practice in general to use MRCI calculations with different symmetry (C2v and Cs in your case)
> to construct the PES, since MRCI may not be invariant (but only slightly) with respect to the choice of the symmetry.
> This is due to how we generate the CI basis functions.
>
> Best wishes,
> Toru
>
> On Mar 24, 2011, at 9:30 PM, Jacky LIEVIN wrote:
>
>> dear users,
>>
>> The input below calculates few points of the potential curve for the rigid umbrella motion of CH3+ in its ground electronic state (2 A2" (D3h) --> 2 B2 (C2v) --> 2 A' (Cs)).
>> The umbrella angle is changed from 90.0 to 90.1 degrees by steps of 0.02 degrees and the results are:
>>
>>  ANGLE         ECASSCF          EMRCI             EMRCIDAV
>>  90.00      -39.61901934   -39.71401806   -39.71754590
>>  90.02      -39.61901934   -39.71401805   -39.71754589
>>  90.04      -39.61901933   -39.71401804   -39.71754588
>>  90.06      -39.61901932   -39.71401903   -39.71754705
>>  90.08      -39.61901930   -39.71401900   -39.71754702
>>  90.10      -39.61901928   -39.71401897   -39.71754699
>>
>> The first point (D3h geometry) is calculated in C2v symmetry while the others (C3v) are calculated in Cs.
>> A sudden stabilization (below the planar equilibrium energy) occurs in the MRCI and MRCI+Davidson curves at 90.06 degrees . Note that the CASSCF curve doesn't exhibit such a feature.
>> Comparison of MRCI calculations below and above 90.06 shows that the number of N-2 electron functions increase from 48 to 49 and that the number of contracted configurations moves accordingly from 17183 to 17310.
>> Would it be possible to control these numbers in order to obtain smooth curves correlating C3v point to planar D3h?
>>
>> Note that this problem occurs in the frequency calculation with as a consequence wrong frequencies (too low) for the out of plane mode.
>>
>> Any ideas about the origin of this symmetry breaking and how to solve it are welcomed?
>>
>>
>> Jacky
>>
>>
>>
>> *** CH3 fondamental
>> gthresh,energy=1.d-8,step=1.d-5
>> gprint,orbitals,civector
>> basis=vdz
>> rx=1.0 ang
>> r=1.09503    ang
>> hx=90.0
>> dhh=0.02
>> hh=hx
>> d=120
>> geometry={C;H2 C r;X1 C rx H2 hh;H3 C r X1 hh H2 d;H4 C r X1 hh H2 -d}
>> angle(1)=hh
>> {hf
>> wf,9,3,1}
>> {multi
>> wf,9,3,1}
>> ecasscf(1)=energy(1)
>> {ci
>> maxiter,50
>> wf,9,3,1}
>> emrci(1)=energy(1)
>> emrcidav(1)=energd(1)
>> do i=2,6
>> hh=hh+dhh
>> symmetry,nosym
>> geometry={C;H2 C r;X1 C rx H2 hh;H3 C r X1 hh H2 d;H4 C r X1 hh H2 -d}
>> hf
>> {multi
>> closed,1
>> start,2140.2
>> wf,9,1,1}
>> angle(i)=hh
>> ecasscf(i)=energy(1)
>> {ci
>> wf,9,1,1}
>> emrcidav(i)=energd(1)
>> emrci(i)=energy(1)
>> enddo
>> table,angle,ecasscf,emrci,emrcidav
>> ---
>>
>>
>> _____________________________________
>> Jacky Liévin
>> Service de Chimie Quantique et Photophysique
>> Université Libre de Bruxelles, CPi 160/09
>> 50 av F.D. Roosevelt
>> B-1050 Bruxelles
>> Belgium
>> Tel: +32-2-650 4089
>> Fax: +32-2-650 4232
>> _____________________________________
>>
>> _______________________________________________
>> Molpro-user mailing list
>> Molpro-user at molpro.net
>> http://www.molpro.net/mailman/listinfo/molpro-user
>

_____________________________________
Jacky Liévin
Service de Chimie Quantique et Photophysique
Université Libre de Bruxelles, CPi 160/09
50 av F.D. Roosevelt
B-1050 Bruxelles
Belgium
Tel: +32-2-650 4089
Fax: +32-2-650 4232
_____________________________________

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