[molpro-user] CCSDT(Q) energy calculation using MRCC Kallay on Molpro

[Peterson, Kirk]

Hi,

one hack you can use is to run your ROHF orbitals through 1 iteration of the UHF program (maxit,1) and then use these in mrcc. You’ll need to add the ignore_error option to the orbital directive in mrcc. This is not entirely rigorous since some terms are then missing in the (Q), but it does generally give very reasonable results.

regards,

-Kirk

On Dec 8, 2017, at 4:54 PM, Shiblee Ratan <shibleeratan at gmail.com<mailto:shibleeratan at gmail.com>> wrote:

Hello Molpro Experts,

Is it possible to do an MRCC Kallay CCSDT(Q) energy calculation for an open-shell ROHF reference? The error message below keeps giving me hope:

Executing mrcc...

 Approximate CC methods are not implemented for standard ROHF orbitals!
 Use semicanonical orbitals!

 Fatal error in mrcc.
 ? Error
 ?  Fatal error in mrcc.
 ? The problem occurs in MRCC


I am trying to calculate the CCSDT(Q) energy for a (doublet-B1) NH2 molecule. Tried a lot of things, but it seems like there is no option to force Molpro to generate semicanonical ROHF orbitals as the error message above wants. ROHF keeps generating canonical/standard orbitals in record file 2100.2.

CCSDT(Q) energy works fine with UHF reference though.

Any help or suggestion to make MRCC Kallay's CCSDT(Q) work with the ROHF reference will be greatly appreciated.

Input file I used is:

-----------------------------------------------------------------------------------------------------------
memory,768,m
gthresh,energy=1.0d-12,orbital=1.0d-12,oneint=1.0d-16,twoint=1.0d-16
Geometry = {
H1
N  ,  H1  , rNH
H2 ,  N   , rNH  ,  H1  ,  aHNH
}

rNH   =    1.04100000 Ang
aHNH  =  100.72710000 Degree

basis=cc-pvdz

{rhf;maxit,100
wf,nelec=9,sym=2,spin=1
orbital,type=semicanonical or pseudo-canonical              <--- Tried these and many other combinations but did not make any difference
occ,3,1,1,0;closed,3,0,1,0}

mrcc,method=ccsdt(q)



-----------------------------------------------------------------------------------------
Dr. Shiblee Ratan Barua
Postdoctoral Research Fellow
Rm S162, Bld 34
NASA Goddard Space Flight Center
8800 Greenbelt Rd, Greenbelt, MD USA 20771
Email: shibleeratan at gmail.com<mailto:shibleeratan at gmail.com>, shiblee.barua at nasa.gov<mailto:shiblee.barua at nasa.gov>
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