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