Nuclear Quantum Effects in Water Clusters: The Role of the Molecular Flexibility
| Autor: | Briesta S. González, Carlos Vega, Luis M. Sesé, Eva G. Noya |
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| Rok vydání: | 2010 |
| Předmět: |
Models
Molecular Tritiated water Chemistry Empirical modelling Structure (category theory) Water Charge density Surfaces Coatings and Films Maxima and minima Kinetics chemistry.chemical_compound Quantum mechanics Physics::Atomic and Molecular Clusters Materials Chemistry Water model Quantum Theory Thermodynamics Molecule Physical and Theoretical Chemistry Monte Carlo Method Path integral Monte Carlo |
| Zdroj: | The Journal of Physical Chemistry B. 114:2484-2492 |
| ISSN: | 1520-5207 1520-6106 |
| DOI: | 10.1021/jp910770y |
| Popis: | With the objective of establishing the importance of water flexibility in empirical models which explicitly include nuclear quantum effects, we have carried out path integral Monte Carlo simulations in water clusters with up to seven molecules. Two recently developed models have been used for comparison: the rigid TIP4PQ/2005 and the flexible q-TIP4P/F models, both inspired by the rigid TIP4P/2005 model. To obtain a starting configuration for our simulations, we have located the global minima for the rigid TIP4P/2005 and TIP4PQ/2005 models and for the flexible q-TIP4P/F model. All the structures are similar to those predicted by the rigid TIP4P potential showing that the charge distribution mainly determines the global minimum structure. For the flexible q-TIP4P/F model, we have studied the geometrical distortion upon isotopic substitution by studying tritiated water clusters. Our results show that tritiated water clusters exhibit an r(OT) distance shorter than the r(OH) distance in water clusters, not significant changes in the Phi(HOH) angle, and a lower average dipole moment than water clusters. We have also carried out classical simulations with the rigid TIP4PQ/2005 model showing that the rotational kinetic energy is greatly affected by quantum effects, but the translational kinetic energy is only slightly modified. The potential energy is also noticeably higher than in classical simulations. Finally, as a concluding remark, we have calculated the formation energies of water clusters using both models, finding that the formation energies predicted by the rigid TIP4PQ/2005 model are lower by roughly 0.6 kcal/mol than those of the flexible q-TIP4P/F model for clusters of moderate size, the origin of this difference coming mainly from the geometrical distortion of the water molecule in the clusters that causes an increase in the intramolecular potential energy. |
| Databáze: | OpenAIRE |
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