Large‐Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia

Malloum, Alhadji; Fifen, Jean Jules; Conradie, Jeanet

doi:10.1002/jcc.26071

Cited by 35 publications

(18 citation statements)

References 69 publications

(165 reference statements)

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“…Malloum studied a series of ammonia clusters [90, 252, 253], including (NH 3 ) 20,30,40,50 and H + (NH 3 ) 18,20,25,30,40,50 . The infrared (IR) spectra computed using these GMs agree quite well with experimental spectra.…”

Section: Applicationsmentioning

confidence: 74%

Global optimization of chemical cluster structures: Methods, applications, and challenges

Zhang

Glezakou

2020

Int J of Quantum Chemistry

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Chemical clusters are relevant to many applications in catalysis, separations, materials, and energy sciences. Experimentally, the structure of clusters is difficult to determine, but it is very important in understanding their chemistry and properties. Computational methods can be used to examine cluster structure, however finding the most stable structure is not simple, particularly as the cluster size increases. Global optimization techniques have long been used to tackle the problem of the most stable structure, but such approaches would have to look for a global minimum, while sampling local minima over the whole potential energy surface as well. In this review, the state‐of‐the‐art theory of global optimization theory is summarized. First, the definition, significance, relation to experiments, and a brief history of global optimization is presented. We then discuss, in more detail, three versatile global optimization methods: the basin hopping, the artificial bee colony algorithm, and the genetic algorithm. We close with some representative application examples of global optimization of clusters since 2016 and the challenges, open questions and opportunities in this field.

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Section: Applicationsmentioning

confidence: 74%

Global optimization of chemical cluster structures: Methods, applications, and challenges

Zhang

Glezakou

2020

Int J of Quantum Chemistry

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“…Investigation of ammonia cluster cations has a long history. − Two kinds of ammonia cluster cations are known from previous studies: protonated (H + (NH 3 ) n ) and unprotonated ((NH 3 ) n + ). The core reactions to form ammonia cluster cations are expressed by eqs and , …”

Section: Introductionmentioning

confidence: 99%

Intramolecular Reactions in Ionized Ammonia Clusters: A Direct Ab Initio Molecular Dynamics Study

Tachikawa

2020

J. Phys. Chem. A

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Ammonia cluster cations are a chemical species that has recently attracted considerable research attention as an ion−molecule reaction species in the planetary atmosphere, surface reaction species in materials chemistry, and super-alkali species. Reactions of the radical cation of an ammonia cluster, [(NH 3 ) n ] + (n = 2−6), following the ionization of the parent neutral cluster, were investigated using direct ab initio molecular dynamics to elucidate the reactions of the ammonia cluster cation under astrochemical conditions. The calculations showed that two competing reaction channelsproton transfer (PT) channel and complex formation channeloperate after the ionization of neutral clusters. In the PT channel, a proton of NH 3 + was transferred to a neighboring ammonia molecule. The PT channel was found in all clusters (n = 2−6). Reaction via the PT channel became faster with increasing cluster size and saturated around n = 5− 6. In the complex formation channel, a face-to-face complex having a H 3 N−NH 3 + structure (with a N−N bond) was formed. This channel was found only in larger clusters (n = 5−6). Time scales of PT and complex formation channels were calculated to be 20− 30 and 40−50 fs, respectively. The reaction mechanism was discussed based on the results of theoretical calculations.

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“…The calculation of the free energies requires the calculation of frequencies; thus, the relative populations are reported in this work at the MN15/6‐31++G(d,p) level of theory. It is worth mentioning that TEMPO has been successfully applied in our previous works to derive the relative populations of neutral and protonated ammonia clusters, hydrated sodium clusters, neutral and protonated methanol clusters, neutral and protonated water clusters and solvated ferrousion and copper ion in ammonia 35‐37,39,70,71 . In those works, the reported relative populations were supported by infrared spectroscopic studies, where good agreements with experiments were found.…”

Section: Resultsmentioning

confidence: 62%

Binding energies and isomer distribution of neutral acetonitrile clusters

Malloum

Fifen

Conradie

2020

Int J of Quantum Chemistry

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Structures and relative stabilities of neutral acetonitrile clusters up to decamer have been investigated. We used the ABCluster code to thoroughly explore the potential energy surfaces (PESs) of the acetonitrile clusters and to generate initial geometries, which are further fully optimized at the MN15/6-31++G(d,p) level of theory. Our exploration yielded several new local and global minima structures of the acetonitrile clusters. We located new global minimum structures of the acetonitrile pentamer to decamer. The results show that the PESs of the acetonitrile clusters are very flat, yielding several isoenergetic structures. Our investigations also revealed that the stability of the acetonitrile clusters is due both to CHÁ Á ÁN and dipole-dipole interactions. Structures stabilized by the latter are found to be more stable than those stabilized by the former at low temperatures. Furthermore, we examined the effect of temperature on the stability of the structures of the acetonitrile clusters for temperatures in the range 20 to 400 K. We found that several structures contribute to the population of the clusters at high temperatures, and also that a significant contribution to the population comes from isomers that lie within 2.0 kcal/mol from the most stable one. In addition, we used the most stable structures to compute the binding energies of the acetonitrile clusters and to assess the performance of some DFT functionals (MN15, ωB97XD, PW6B95D3, and B2PLYP) in comparison with the MP2 method associated to the aug-cc-pVTZ basis set in calculating the binding energies. We found that the MN15 functional performs better than ωB97XD and PW6B95D3, and that MN15 is less sensitive to the basis set change. We also used an extrapolation scheme to calculate the binding energies of the acetonitrile clusters at the highly accurate W1BD, CBS-QB3, and G4MP2 levels of theory. The resulting binding energies are recommended for future benchmarking of the acetonitrile clusters. K E Y W O R D S acetonitrile clusters, binding energy, DFT functionals, molecular clusters, relative energy, temperature effects, ABCluster code

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Large‐Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia

Cited by 35 publications

References 69 publications

Global optimization of chemical cluster structures: Methods, applications, and challenges

Global optimization of chemical cluster structures: Methods, applications, and challenges

Intramolecular Reactions in Ionized Ammonia Clusters: A Direct Ab Initio Molecular Dynamics Study

Binding energies and isomer distribution of neutral acetonitrile clusters

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