Single-molecule magnets are perspective materials for molecular spintronic applications. Predictions of magnetic coupling in these systems have posed a long standing problem, as calculations of this kind require a balanced description of static and dynamic electron correlation. The large size of these systems limits the choice of theoretical methods used. Two methods feasible to predict the exchange coupling parameters are broken symmetry Density Functional Theory (BSDFT) and DFT with empirical Hubbard U parameter (DFT+U). In this contribution we apply DFT+U to study Mn-based molecular magnets using Vanderbilt Ultrasoft Pseudopotential plane wave DFT method, implemented in Quantum ESPRESSSO code. Unlike most previous studies, we adjust U parameters for both metal and ligand atoms using two dineuclear molecular magnets [Mn
as the benchmarks. Next, we apply this methodology to Mn
molecular wheel. Our study finds antiparallel spin alignment in weakly interacting fragments of Mn
, in agreement with experimental observations.