Controlling the structure (or polymorph) in which a molecule crystallizes is a long-standing issue. Since polymorphs have different physical properties, it is crucial for many applications to control which polymorphs form during crystallization. We develop hybrid Monte Carlo methods and apply them to study polymorph selection during crystal nucleation and growth. We perform two different types of simulation methods corresponding to the two steps of nucleation and growth. Crystal nucleation is an activated process. Therefore, we combine these hybrid methods with a non-Boltzmann sampling technique (the so-called umbrella sampling technique) and an appropriate reaction coordinate. Once we have formed a crystal nucleus of a critical size, we carry out hybrid simulations of the growth from the crystal nucleus without applying any bias potential. We illustrate these methods on a series of examples.

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