Hi Arnab, thanks for trying some more things and printing out the MPS (in order to see it's bond dimension 1). So the issue is that you have not set any DMRG accuracy / sweeping parameters besides the number of sweeps. If you add a line like:
before you call DMRG then the bond dimension will be allowed to grow. I'd also recommend setting a cutoff, such as
Hope that fixes things! Good idea to do 50 sweeps for an excited state. It's best to do at least 20 for those, or as many as needed until the energy is barely changing in the last 5 sweeps or so.