McCulloch, I PGulacsi, Miklos2015-12-100950-0839http://hdl.handle.net/1885/65568A new density matrix renormalization group (DMRG) algorithm is presented which conserves the total spin. This is the first time that standard DMRG is extended to exploit fully the symmetries of the Hamiltonian. The obtained general procedure works for any operator, even operators that do not commute with the Hamiltonian. The new method gives substantial improvements over the standard DMRG.Keywords: Algorithms; Ground state; Hamiltonians; Phase transitions; Thermodynamics; Density matrix renormalization group (DMRG); Quantum theory200110.1080/095008301100400092015-12-10