On May 12, 2009, at 5:15 AM, khalid hassan wrote:

Dear alps team

I am using the print_numeric program in the model directory to print the basis vectors and hamiltonian matrices for the fermionic hubbard model.

Now the problem is that the basis gives the specified combination but not the correct sign.

for example for 2 site hubbard model one up spin, one down spin it gives

{ [ |0 0 > |1 1 > ] [ |0 1 > |1 0 > ] [ |1 0 > |0 1 > ] [ |1 1 > |0 0 > ] }

now the 2nd and 3rd row should have opposite sign either 2nd -ve or 3rd negative according to convention.

Why should a basis vector have a negative sign? You can choose any basis you want, and above is our choice.

Now based on this set it calculated the matrix

[4,4]((0,1,-1,0),(1,0,0,1),(-1,0,0,-1),(0,1,-1,0))

which is wrong as all terms are negative. so I cannot find correct eigen values from this matrix.

In above matrix not all terms are negative, and they should not all be negative, since there is a + sign when you exchange two fermions.

tell me how can I solve the problem with sign problem of basis states and find correct hamiltonian matrix

Can you please clarify what the problem is?

Matthias