PREDICTING POLYMORPHISM AT FINITE TEMPERATURE USING METADYNAMICS Urea Naphthalene 0 50 100 Form I Form B Form IV Form A Liquid Partially ordered 1 Form I Form II Liquid Partially ordered 2 We clustered the configurations of the atomistic trajectory using a hierarchical clustering algorithm. We also clustered the configurations of naphthalene. In this case many partially ordered structures are identified. Pablo Piaggi and Michele Parrinello EPFL, ETHZ, USI Switzerland We introduce a computational method to discover polymorphs in molecular crystals at finite temperature. The method is based on reproducing the crystallization process starting from the liquid and letting the system discover the relevant polymorphs. This idea, however, conflicts with the fact that crystallization has a time scale much longer than that of molecular simulations. In order to bring the process within affordable simulation time, we enhance the fluctuations of a collective variable by constructing a bias potential with well tempered metadynamics. We use as collective variable an entropy surrogate based on an extended pair correlation function that includes the correlation between the orientation of pairs of molecules. The National Centres of Competence in Research (NCCR) are a research instrument of the Swiss National Science Foundation r (nm) Polymorph I 0.0 0.5 1.0 0 π π 0 20 60 80 40 2 θ New polymorph - Form A New polymorph - Form B Method References: [1] P. M. Piaggi, O. Valsson, and M. Parrinello, Physical Review Letters 119, 015701 (2017) [2] A. Barducci, G. Bussi, and M. Parrinello, Physical Review Letters 100, 020603 (2008) r (nm) Liquid 0.0 0.5 1.0 0 1 2 3 4 5 0 π π 2 θ We shall consider a system of molecules and, for the purpose of developing a collective variable, we shall represent each molecule by the position of its center of mass and a vector that characterizes its orientation in space. The pair entropy[1] of such a system is: We use this function as collective variable in a well-tempered metadynamics simulation[2]. For urea the angles θ are defined from the vectors: Extended pair correlation function 0 60 120

PREDICTING POLYMORPHISM AT FINITE TEMPERATURE … · PREDICTING POLYMORPHISM AT FINITE TEMPERATURE USING METADYNAMICS Urea Naphthalene 0 50 10 0 Form I Form B Form IV Form A Liquid

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PREDICTING POLYMORPHISM AT FINITE TEMPERATURE USING METADYNAMICS

Urea

Naphthalene

10 0

Form I Form B Form IV Form A Liquid

Partially ordered 1 Form I Form IILiquid Partially

ordered 2

We clustered the configurations of the atomistic trajectory using a hierarchical clustering algorithm.

We also clustered the configurations of naphthalene. In this case many partially ordered structures are identified.

Pablo Piaggi and Michele ParrinelloEPFL, ETHZ, USI Switzerland

We introduce a computational method to discover polymorphs in molecular crystals at finite temperature. The method is based on reproducing the crystallization process starting from the liquid and letting the system discover the relevant polymorphs. This idea, however, conflicts with the fact that crystallization has a time scale much longer than that of molecular simulations. In order to bring the process within affordable simulation time, we enhance the fluctuations of a collective variable by constructing a bias potential with well tempered metadynamics. We use as collective variable an entropy surrogate based on an extended pair correlation function that includes the correlation between the orientation of pairs of molecules.

The National Centres of Competence in Research (NCCR) are a research instrument of the Swiss National

Science Foundation

r (nm)Po

lym

orph

I0.0 0.5 1.0

402θ

New polymorph - Form A

New polymorph - Form B

Method

References:[1] P. M. Piaggi, O. Valsson, and M. Parrinello, Physical Review Letters 119, 015701 (2017)[2] A. Barducci, G. Bussi, and M. Parrinello, Physical Review Letters 100, 020603 (2008)

r (nm)

Liqu

0.0 0.5 1.0012345

2θ

We shall consider a system of molecules and, for the purpose of developing a collective variable, we shall represent each molecule by the position of its center of mass and a vector that characterizes its orientation in space. The pair entropy[1] of such a system is:

We use this function as collective variable in a well-tempered metadynamics simulation[2]. For urea the angles θ are defined from the vectors:

Extended pair correlation function

120