Matthias, et al.,

Could you please post how to code this for one, two, three and four spins?  From there I should be able to extend it out to N spins.  I’ll likely be working with N<=16.

Thanks,

Matt Stone

>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

>>