Dear Matthias, Thank you very much for your reply. I have solved the problem with my own DMRG code. However, I will keep tracking ALPS project. It is indeed very great. Thank you for your work. 2011/3/25 <comp-phys-alps-users-request@lists.phys.ethz.ch>

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Today's Topics:

1. Re: How to define an operator A in "models.xml" (Matthias Troyer) 2. multiple eigenvalues (degenerate eigenstates) in sparsediag (Andriy Zhugayevych)

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Message: 1 Date: Thu, 24 Mar 2011 12:28:28 -0500 From: Matthias Troyer <troyer@phys.ethz.ch> Subject: Re: [ALPS-users] How to define an operator A in "models.xml" To: comp-phys-alps-users@lists.phys.ethz.ch Message-ID: <DAC79DA4-5BC5-49DA-BAAE-1B885B6736BB@phys.ethz.ch> Content-Type: text/plain; charset="utf-8"

Dear Sunzhaoyu,

This is not implemented yet. For now you will have to decompose it into more elementary operators.

Matthias

On Mar 18, 2011, at 12:38 AM, ??? wrote:

...

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