Dear ALPS users and developers
I want to re-produce the result of a 12x2 spin ladder with four-site interaction. The four-site interaction is between two nearest-neighboring rungs. Please see: [ Phys. Rev. B 74, 155119 (2006), http://prb.aps.org/abstract/PRB/v74/i15/e155119 ]
However, it seems that ALPS 2.0 do not support 4-site terms. Thus I define every rung as a single site, then the ladder becomes a one-dimensional chain (local degree of freedom is 4), and the four-site interaction becomes a two-site interaction.
In original ladder, the SITEBASIS is just {sz} = {-1/2, 1/2}. In this basis operators such as Sminus have very compact expressions thus they can be simply define as: <OPERATOR name="Sminus" matrixelement="sqrt(S*(S+1)-Sz*(Sz-1))">
However, in the new model, a possible choice of SITEBASIS is {J,Jz}={00, 1-1, 10, 11}. In this new basis, operators do not have very compact expressions, however, the elements of the operator can be easily obtained through unitary transformation. The problem is, I can figure out all the elements of an operator in basis{J, Jz}, but I do not know how to define the operator in "models.xml".
In other words, suppose an operator X in basis {J, Jz} is explicitly found to be [ 1, 0, 0, 0 0, 2, 1, 0 0, 1, 3, 0 0, 0, 0, 4] then in ALPS 2.0, is it possible to define X by simply writing down every elements Xij in "models.xml" ?
Any suggestion would be appreciated.
sunzhaoyu