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

[Shiblee Ratan]

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, shiblee.barua at nasa.gov
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