Hi Vipin,
How do you choose your chemical potential? Note that in the parameter file below you dud not fix the number of particles. DId you want the number of particles fixed to 2?
Matthias
On 19 Feb 2010, at 07:01, Vipin Varma wrote:
Hi
I am trying the Lanczos method for solving the Bose-Hubbard model on a square lattice, to get the t/U dependence of the ground state energy per site. I tried a simple 2x1 cluster with open and periodic boundary conditions and I get a linear dependence for the energy on t/U; analytically (which I am reasonably sure is correct), I get a parabolic dependence for the energy on t/U, if I consider 2 bosons over 2 sites.
Here is my parameter file:
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LATTICE_LIBRARY="../lattices.xml"; LATTICE="square lattice";
MODEL_LIBRARY="../models.xml"; MODEL="boson Hubbard"; U = 1; Nmax = 2; L=2; W =1; {t=0.1;} {t=0.01;} {t=0.02;} {t=0.03;} {t=0.04;} {t=0.05;} {t=0.06;} {t=0.07;} {t=0.08;} {t=0.09;}
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I have tried Nmax = 2,4,6, but all give me a linear dependence; also strangely, the energy range does not change much when I vary the value of U by orders of magnitude.
I guess I am missing something simple. Any ideas will be appreciated.
Vipin