On 29 May 2009, at 19:09, Su Chun-Hsu wrote:
Dear all, I'm new to using ALPS and not entirely confident with setting up my model, which didn't appear to work at the moment. I'm interested in polaritonic system -- evanescently coupled-cavity system, each cavity containing a two-level atom. I have set up my model in the attached xml, Sminus and Splus are atomic projection operators and b are photon annihilation operator. The total number of excitations (atomic and photonic) is conserved. When I try running it, there is an bad_alloc error. Will anyone be kindly give me some pointers? Much appreciated and thank you very much in advance.
Not knowing exactly what you have in mind I can only say that the model looks reasonable. You have to be very careful though as you have a large number of local states and already a 2x2 lattice without constraints has a Hilbert space of 202^4, which is far too large to be solved by exact diagonalization.
With your constraints the Hilbert space is smaller but there is still the problem that the ALPS program wants to build the full Hamiltonian matrix for two sites. The 2-site Hilbert space in your model is 202^2 = 40804 states. The matrix for two sites thus 40804 x 40804 = 1 664 966 416 elements large, which needs 12.5 GB memory. The allocation of this matrix fails and thus there is a bad_alloc exception. Such a model is to big to be studied by exact diagonalization. If you reduce the maximum occupancy t0 10 or 20 it will work
Matthias