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Spin-orbit matrix elements and eigenstates can be computed using either the Breit-Pauli (BP)
operator or spin-orbit pseudopotentials (ECPs).
The *state-interacting* method is employed, which means that the
spin-orbit eigenstates are obtained by diagonalizing
in a basis of eigenfunctions of .
The full Breit-Pauli SO-operator can be used only for MCSCF wavefunctions. For MRCI wavefunctions,
the full BP operator is used for computing the matrix elements between *internal configurations*
(no electrons in external orbitals), while for contributions of external configurations a mean-field
one-electron fock operator is employed. The error caused by this approximation is usually smaller
than 1 cm.
The program allows either the computation of individual spin-orbit matrix elements for a given pair of
states, or the automatic setting-up and diagonalization of the whole matrix for a given set of
electronic states. In the latter case, matrix elements over one-electron operators
are also computed and transformed to the spin-orbit eigenstates (by default, the dipole matrix
elements are computed; other operators can be specified on the `GEXPEC` or `EXPEC` cards,
see section 6.13). Since it may be often sufficient to compute the spin-orbit matrix
elements in a smaller basis than the energies, it is possible to replace the energy eigenvalues
by precomputed values, which are passed to the spin-orbit program by the MOLPRO
variable `HLSDIAG`.

** Next:** 44.2 Calculation of SO
** Up:** 44 SPIN-ORBIT-COUPLING
** Previous:** 44 SPIN-ORBIT-COUPLING
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molpro@molpro.net 2018-03-22