(86c) An Atomistic Lattice Dynamics Approach for Free Energy Calculations within Crystal Structure Prediction Studies
- Conference: AIChE Annual Meeting
- Year: 2020
- Proceeding: 2020 Virtual AIChE Annual Meeting
- Group: Computational Molecular Science and Engineering Forum
- Time: Monday, November 16, 2020 - 8:30am-8:45am
Recent advances in CSP were highlighted in the last blind test organised by Cambridge Crystallographic Data Centre2. It is worth noting that only 7 out of the 25 groups participating in the last test have incorporated FE calculations within their workflow, while the remaining groups used only lattice energy in their predictions, thus neglecting temperature and vibrational effects. Lattice dynamics (LD) theory was deployed successfully for the evaluation of vibrational free energies, utilizing either dispersion-corrected periodic density functional theory3,4 (DFT-d) or force field methods based on distributed multipoles expansion5,6,7 (DMA). DFT-d can provide very accurate results at a high computational cost, whereas the DMA-based approach provides a good trade-off between accuracy and efficiency but cannot account for internal modes arising from intramolecular vibrations. A limitation of both methods is that they rely on the construction of supercells, which increases computational demands and results in some ambiguity in the generation of dispersion curves.
In this work, we present a recently-developed methodology8 for performing atomistic lattice dynamics calculations, which is suitable for conducting FE calculations for a large number (>100) of structures generated in CSP studies. This methodology is based on LD theory within the harmonic approximation, with intramolecular interactions quantified by isolated quantum mechanical calculations9. The intermolecular interactions are partitioned into electrostatics and repulsion/dispersion interactions and are modelled using ab initio distributed multipoles and a semi empirical potential, respectively. To illustrate the approach, we apply a multistage CSP methodology to tetracyanoethylene (C6N4), a small planar molecule. The global search stage is performed using the CrystalPredictorII10,11 for the generation of candidate structures. The lowest energy structures, within 20kJ/mol from the global minimum in lattice energy, are minimised atomistically using CrystalOptimizer12 yielding 837 unique structures after clustering. We evaluate the vibrational free energy of the 200 most promising structures, using our in-house LD algorithm8, for the determination of polymorphic stability, entropy, heat capacity and thermal energy in a temperature range between 0 and 400K.
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(2) Reilly, A. M.; Cooper, R. I.; Adjiman, C. S.; Bhattacharya, S.; Boese, A. D.; Brandenburg, J. G.; Bygrave, P. J.; Bylsma, R.; Campbell, J. E.; Car, R.; et al. Report on the Sixth Blind Test of Organic Crystal Structure Prediction Methods. Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater. 2016, 72, 439â459.
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(7) Stone, A. J. Distributed Multipole Analysis, or How to Describe a Molecular Charge Distribution. Chem. Phys. Lett. 1981, 83, 233â239.
(8) Vasileiadis, M. Calculation of the Free Energy of Crystalline Solids, Imperial College London, 2013.
(9) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenb, D. J. al. Gaussian 09, 2009.
(10) Habgood, M.; Sugden, I. J.; Kazantsev, A. V.; Adjiman, C. S.; Pantelides, C. C. Efficient Handling of Molecular Flexibility in Ab Initio Generation of Crystal Structures. J. Chem. Theory Comput. 2015, 11, 1957â1969.
(11) Sugden, I.; Adjiman, C. S.; Pantelides, C. C. Accurate and Efficient Representation of Intramolecular Energy in Ab Initio Generation of Crystal Structures. I. Adaptive Local Approximate Models. Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater. 2016, 72, 864â874.
(12) Kazantsev, A. V.; Karamertzanis, P. G.; Adjiman, C. S.; Pantelides, C. C. Efficient Handling of Molecular Flexibility in Lattice Energy Minimization of Organic Crystals. J. Chem. Theory Comput. 2011, 7, 1998â2016.
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