For many spins you need to code each number of spins separately, but it gets ugly pretty soon.

Matthias

On 24 Jan 2012, at 19:36, Stone, Matthew B. wrote:

Has anyone written an ALPS operator for the operator S^2 for a general number of spins in a system?

For example, I would like to list the Sztotal and S^2 values for different energy levels calculated.

The S^2 operator can be written as S^2 = (S_1 + S_2 + S_3 +…)^2 where S_1, S_2, etc. are the vector operators.

for two spins one can write this as S^2 = (S_1 + S_2)^2 = (S_1)^2 + (S_2)^2 + 2 S_1 \dot S_2 = s(s+1) + s(s+1) + 2S_{1z}S_{2z} + S_{1+}S_{2-} + S_{1-}S_{2+}

But I don’t see how to generalize this for a system of many spins using the ALPS “spin” sitebasis and basis in order to have this operator value listed in the output calculations.

Any help would be appreciated. Thanks,

Matthew B. Stone Neutron Scattering Science Division Oak Ridge National Laboratory PO box 2008 MS6475 Oak Ridge, TN 37831-6475

Phone: 1-865-202-6898 Fax: 1-865-574-6080