Structure and thermodynamics of H3O+(H2O)8 clusters: A combined molecular dynamics and quantum mechanics approach

Temelso, Berhane; Köddermann, Thorsten; Kirschner, Karl K.; Klein, Katurah L.; Shields, George C.

doi:10.1016/j.comptc.2013.07.039

Cited by 13 publications

(9 citation statements)

References 106 publications

(142 reference statements)

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“…11,12 Such a procedure makes sense, since the standard combination rules of Eq. (19) are completely heuristic, and there is a-priori no reason why they should work for every combination of atoms.…”

Section: Hydroxidementioning

confidence: 99%

Optimization of classical nonpolarizable force fields for OH− and H3O+

Bonthuis

Mamatkulov

Netz

2016

The Journal of Chemical Physics

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We optimize force fields for H3O(+) and OH(-) that reproduce the experimental solvation free energies and the activities of H3O(+) Cl(-) and Na(+) OH(-) solutions up to concentrations of 1.5 mol/l. The force fields are optimized with respect to the partial charge on the hydrogen atoms and the Lennard-Jones parameters of the oxygen atoms. Remarkably, the partial charge on the hydrogen atom of the optimized H3O(+) force field is 0.8 ± 0.1|e|--significantly higher than the value typically used for nonpolarizable water models and H3O(+) force fields. In contrast, the optimal partial charge on the hydrogen atom of OH(-) turns out to be zero. Standard combination rules can be used for H3O(+) Cl(-) solutions, while for Na(+) OH(-) solutions, we need to significantly increase the effective anion-cation Lennard-Jones radius. While highlighting the importance of intramolecular electrostatics, our results show that it is possible to generate thermodynamically consistent force fields without using atomic polarizability.

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Section: Hydroxidementioning

confidence: 99%

Optimization of classical nonpolarizable force fields for OH− and H3O+

Bonthuis

Mamatkulov

Netz

2016

The Journal of Chemical Physics

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“…Once the vibrational frequencies are obtained from an ab initio computation, the temperature-dependent entropy term can be assessed in the so-called harmonic superposition approximation . This has been done routinely for, e.g., water clusters and charged water clusters, and most extensively for protonated water − and methanol clusters. , For the hydrated sodium cation clusters, entropy-driven isomers were investigated (as a function of T ) by Miller and Lisy, but only for n = 4.…”

Section: Introductionmentioning

confidence: 99%

Structure and Spectroscopy of Hydrated Sodium Ions at Different Temperatures and the Cluster Stability Rules

Fifen

Agmon

2016

J. Chem. Theory Comput.

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The sodium cation plays an important role in several physiological processes. Understanding its solvation may help understanding ion selectivity in sodium channels that are pivotal for nerve impulses. This paper presents a thorough investigation of over 75 isomers of gas-phase Na(+)(H2O)(n=1-8) clusters, whose optimized structures, energies, and (harmonic) vibrational frequencies were computed quantum mechanically at the full MP2/6-31++G(d,p) level of theory. From these data, we have calculated the temperature effects on the cluster thermodynamic functions, and thus the equilibrium Boltzmann distribution for each n. For a selected number of isomers, we have corrected the calculations for basis set superposition error (BSSE) to obtain accurate clustering energies, in excellent agreement with experiment. The computed clusters are overwhelmingly 4-coordinated, as opposed to bulk liquid water, where sodium cations are believed to be mostly 5- or 6-coordinated. To explain this, we suggest the "cluster stability rules", a set of coordination-number-dependent hydrogen-bond (HB) strengths that can be obtained using a single BSSE correction. Assuming additivity and transferability, these reproduce the relative stability of most of our computed isomers. These rules enable us to elucidate the trends in HB strengths, outlining the major determinants of cluster stability. For n = 4 and 5, we have also performed anharmonic vibrational calculations (VPT2) to compare with available photodissociation infrared spectra of these gas-phase clusters. The comparison suggests that the experiments actually monitor a mixture of predominantly 3-coordinated isomers, which is quite remote from the computed Boltzmann distribution, particularly at low temperatures. Surprisingly, for these experiments, water evaporation pathways can rationalize the non-equilibrium isomer distribution. The equilibrium isomer distribution is, in turn, rationalized by the entropy of internal rotations of "dangling" water molecules.

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“…of species embedded in ammonia) involving gas or liquid phase ammonia. Moreover, despite the fact that it is well-known that hydrogen-bond structures in neutral water clusters, 27 charged water clusters, 28 protonated water clusters [29][30][31][32][33][34] and protonated methanol clusters 35,36 are entropy-driven, no work has investigated the temperature effects on the structures of ammonia clusters. In regard to all these missing information on structures of ammonia clusters, further investigations of ammonia clusters in various ranges of temperatures are needed.…”

Section: Introductionmentioning

confidence: 99%

Structures and relative stabilities of ammonia clusters at different temperatures: DFT vs. ab initio

Malloum

Fifen

Dhaouadi

et al. 2015

Phys. Chem. Chem. Phys.

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A hydrogen bond network in ammonia clusters plays a key role in understanding the properties of species embedded in ammonia. This network is dictated by the structures of neutral ammonia clusters. In this work, structures of neutral ammonia clusters (NH3)n(=2-10) have been studied at M06-2X/6-31++G(d,p) and MP2/6-31++g(d,p) levels of theory. The analysis of the relative stabilities of various hydrogen bond types has also been studied and vibrational spectroscopy of the ammonia pentamer and decamer is investigated. We noted that M06-2X provides lower electronic energies, greater binding energies and higher structural resolution than MP2. We also noted that at the M06-2X level of theory, the binding energy converges to the experimental vaporization enthalpy faster than that at the MP2 level of theory. As a result, it is found that the M06-2X functional could be more suitable than the MP2 ab initio method in the description of structures and energies of ammonia clusters. However, we found that the electronic energy differences obtained at both levels of computation follow a linear relation with n (number of ammonia molecules in a cluster). As far as the structures of ammonia clusters are concerned, we proposed new "significant" isomers that have not been reported previously. The most remarkable is the global minimum electronic energy structure of the ammonia hexamer, which has an inversion centre and confirms experimental observation. Moreover, we reported the relative stabilities of neutral ammonia clusters for temperatures ranging from 25 to 400 K. The stability of isomers changes with the increase of the temperature. As a result, the branched and less bonded isomers are the most favored at high temperatures and disfavored at low temperatures, while compact and symmetric isomers dominate the population of clusters at low temperatures. In fine, from this work, the global minimum energy structures of ammonia clusters are known for the first time at a given temperature (T ∼ 0-400 K) and at a reliable computational level of theory.

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Structure and thermodynamics of H3O+(H2O)8 clusters: A combined molecular dynamics and quantum mechanics approach

Cited by 13 publications

References 106 publications

Optimization of classical nonpolarizable force fields for OH− and H3O+

Optimization of classical nonpolarizable force fields for OH− and H3O+

Structure and Spectroscopy of Hydrated Sodium Ions at Different Temperatures and the Cluster Stability Rules

Structures and relative stabilities of ammonia clusters at different temperatures: DFT vs. ab initio

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