TeNPy Forum

Hello, I am trying to evaluate these quantities here: N_a=<\sum_{i}b_{i}^{\dagger}b_{i+1}> ; N_d= <\sum_{i}(b_{i}^{\dagger})^{2}(b_{i+1})^{2}> I have obtained the operators b_{i}^{\dagger}; b_{i+1} using ops = ['Bd'] * model_params['L'] and opss=['B']*model_params['L'] And to find N_a I wrote def Na...

More: what should I write to evaluate\(<e^{i\pi(1-n_{4})}...e^{i\pi(1-n_{30})}>\) in a \(N=36\) Bose-Hubbard model. Basically I want to arbitrarly choose the first and last site of the product. Thanks!

Hello, thanks for the long answer and clarification!
I was wondering if Could be used to evaluate \(<e^{(i\pi(1-n_4)}...e^{(i\pi(1-n_{36}))}>\)

Hello all, I am trying to implement <e^{\sum_{i<j}(\mathbb{1}-n_i)}> . For instance for j=36 . I am trying to do it using Bose-Hubbard model and tried to write it as: N=36 model_params = { "L": N, "t": 1.0, "U": 0.0, "n_max": 4, "bc_MPS": "finit...

Hello all, I am trying to implemente the correlation function $$<b_{i}^\dagger b_{j}>-<b_{i}^\dagger><b_{j}>$$ (with i=4 and j goes from 4 to 46) where the last number is the value of L in model_params like this: model=BoseHubbarModel(model_params) init_state = ['1'] * model.lat.N_sites psi = MPS.fr...

Hey, still sorry for bothering! Actually there's something I am not really getting: 1) alpha = model_params.get('alpha', np.pi, 'real') N_diag = np.arange(site.Nmax + 1) site.add_op('P_alpha', np.diag(np.exp(1.j * alpha * N_diag)), permute_dense=True) Could you please explain me what these 3 lines d...

Thanks, it works!

Thanks again! I do appreciate your help! Just one last thing: how would you implement something like $$-\tau \sum_{\langle i,j \rangle i<j} e^{i \alpha\, n_i}\left( b_i^\dagger b_j + b_j^\dagger b_i \right)$$ where alpha is just a generic number. So basically this accounts to taking the BH Hamiltoni...

Hello, thanks for the answer. Actually I do not want to add a new term in the Hamiltonian but simply modify the first one by putting the parity operator just after the sum symbol and before b_i+bj +h.c.
I dont know if I've been clear!

Hello, I would like to change the Bose-Hubbard Model such that in the first sum in can add \exp{(j*\pi*n_{i})} , where ni is the number operator acting on the i site. How can I do this? I was thinking about working on this part of the classe: def init_terms(self, model_params): # 0) Read and set par...

Hello, thanks for your reply.
Yes, I meant in the ground state! What would be the complete code line?

Hello everyone,
I have a simple question (I guess). I'm trying to find the expectation value of the number operatore using the BH model but I'm really stuck. Does anyone know how to do it? Thanks!