The determinationof molecular conformations, based on energy minimization, has to overcome the presence of multiple minima in the energy surface. Thus the need to reckon on efficient global optimization methods. Here, we are concerned with two models : one for peptide molecules that takes into account Lennard-Jones (L-J), hydrogen bonding, electrostatics and torsional terms, and another for atomic clusters that only considers L-J potentials. We discuss our experience when solving these models with global optimization methods different in nature : the exponential tunneling algorithm, which is deterministic and stochastic procedures based on the simulated annealing concept. these methods have found improved conformations for atomic clusters and for small peptide molecules, respectively and as such, they appear as suitable tools in this context.