Hi all,

In furtherance to my question on using complex variables for the hopping parameter in the input file, I tried to run a very small calculation for the Hubbard model using Exact Diagonalization for L=4 at half filling for t = exp (I x) for different values of x.I performed the same calculation for DMRG and I obtained completely different results.ED gave what is to be expected using Bethe Ansatz solutions at half filling but at any other filling, the results are weird.The surprising thing is that DMRG results are completely different from those obtained by ED.The question is that can one actually represent complex variables in the input file?Going through some notes on the website ( Introduction to ALPS XML S. Todo), it actually says the complex parts can be expressed as "I" which was what I did.Then what may be the reason in the dicrepancy between DMRG and ED results?If there is need I will be ready to send in the plots of the 2 results.

This may rather be a naive question:For a 1D periodic system, despite the fact that I request that it print the total occupation on each site in the input file, it didnt do so in the output.Although the occupation is trivial as it will be the same for all the site but I was just wondering why it didnt print it but it did print it for a chain.

I will be grateful for your answers.

Thanks

Akin

2008/11/24 Akinlolu Akande akandea@tcd.ie

Hi all,

I am a new user of the ALPS package.I successfully installed the package on our machines and I have run some examples in the tutorial directory.

I have 2 questions:

1.For a 1D Hubbard model with a complex 't' (hopping) parameter, is it ok to make t complex in the input file?I actually did a run where I used the following input file for the full diagonalization:

LATTICE="open chain lattice";

LATTICE_LIBRARY="/home/aakande/alps-applications-1.3.3/tutorial/lattices.xml" SWEEPS=5 MAXSTATES=30 CONSERVED_QUANTUMNUMBERS="Nup,Ndown" { MODEL="fermion Hubbard"; MODEL_LIBRARY="/home/aakande/alps-applications-1.3.3/tutorial/models.xml" L=4, Nup_total=1, Ndown_total=1 t=exp(I*5) U=4 NUMBER_EIGENVALUES=1 }

which actually gave some results but I just want to confirm if the results obtained with such input are ok.

2.How does one adjust the input file for a site dependent parameters model?For example, I am interested in a 1D Hubbard model with 10-site chain for which the U term on the first 5 sites are different from the remaining 5 sites (ie 1st 5 sites have U=U1 and the last 5 sites have U=U2) with a different hopping parameter linking the 2 sets of sites.What will change in the input file for such a site dependent model?

Best regards.

Akin