Extended Stevens operators.

Op = stev(S,[k,q])
Op = stev(S,[k,q,iSpin])
Op = stev(__,'sparse')

This function computes matrix representations of the extended Stevens operators for a spin with spin quantum number S. If S is a vector representing the spins of a spin system, the operator matrix is computed for the spin number iSpin in the state space of the full spin system, e.g. the second spin if iSpin==2.

The parameters k and q specify the operator component . Possible values are 0<=k<=2S and q=-k,...,k. k is the rank of the operator, and q is the component. Positive and negative q correspond to cosine and sine components, respectively. The function supports k values between 0 and 12.

For explicit expressions of some common Stevens operators see the page on high-order spin operators.

The cosine tesseral operator component for a spin S=2 is

stev(2,[4,2])

ans =
         0         0    7.3485         0         0
         0         0         0  -12.0000         0
    7.3485         0         0         0    7.3485
         0  -12.0000         0         0         0
         0         0    7.3485         0         0

The value 7.3485 corresponds to .

The extended Stevens operators are computed using Racah's commutator rule for the components of spherical tensor operators and Ryabov's general formula for extended Stevens operators. See I.D.Ryabov, J.Magn.Reson. 140, 141-145 (1999).

spin operators, isto, sop