# [molpro-user] Spin-orbit coupling between Triplet and Singlet states

Kelvin Lee kin.lee at unsw.edu.au
Thu May 7 06:52:04 BST 2015

```Dear Molpro mailing list,

I am trying to learn how to calculate the spin-orbit matrix element
between a singlet and triplet state. As a starting point, I've been
trying to calculate CH2 using CASSCF and MRCI, as there is a lot of
published data on this molecule.

I've tried following the example given in the manual on the S-atom, but
the results I'm getting on CH2 make very little sense to me, and I'd
appreciate it if anyone would extend their help.

My input is as follows:

***,Calculating spin-orbit coupling of CH2
memory,148,M
angstrom
nosym
geom={
C
H1 C rCH
H2 C rCH H1 aHCH
}
RCH=                 1.12276332 ANGSTROM
AHCH=              102.15789308 DEGREE
basis=dzp
{uhf;occ,5;wf,8,0,2         ! UHF of triplet ground state
orbital,4400.1
}
{multi;occ,10;wf,nelec=8,spin=2;wf,nelec=8,spin=0}

{ci;wf,nelec=8,spin=2;save,4500.1}        ! triplet wavefunction
{ci;wf,nelec=8,spin=0;save,4600.1}        ! singlet wavefunction

{ci;tranls,4500.1,4600.1}                 ! calculate matrix element

Which, at the end of the output gives me:

Spin-orbit matrix elements for mean field operator:

!MRCI expec <1.1|LSZ|1.1>     0.000000000000i au =     0.000000006576i
cm-1

If I'm interpreting this correctly, this is supposed to be my matrix
element for these two states?
The previously calculated values lie around ~12 cm-1 or so, so what
unbelievably stupid mistake am I making?

Any form of help would be greatly appreciated.

Thank you,

Kelvin

--

KIN LONG KELVIN LEE | PhD Student
Molecular Photonics Group | School of Chemistry | Faculty of Science
University of New South Wales
Room 417, Chemical Sciences Building F10 | NSW | AUSTRALIA |2052
T9385-0457 |
Ekin.lee at unsw.edu.au  |

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