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

Malloum, Alhadji; Fifen, Jean Jules; Dhaouadi, Zoubeida; Engo, S. G. Nana; Jaı̈dane, N.

doi:10.1039/c5cp03374h

Cited by 64 publications

(44 citation statements)

References 77 publications

(128 reference statements)

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“…Furthermore, we have noted in our previous work that the difference between the electronic energies of the most stable structures of the neutral ammonia clusters computed at two different levels of theory increases (or decreases) linearly as a function of the cluster size n. 35 In the present work, we have observed the same trend for the structures of the neutral acetonitrile clusters (see Figure S1 as an example) We have used this behavior to extrapolate the binding energies of the acetonitrile clusters by computing only the electronic energy of the monomer and that of the dimer at B2PLYP, 28 CBS-QB3, 42 W1BD, 43 and G4MP2 44 levels of theory. CBS-QB3, W1BD, and G4MP2 use several and successive steps to compute highly accurate energy of a given system (Table S1).…”

Section: Binding Energiesmentioning

confidence: 83%

“…Tempo code were first published in our work on the structures of protonated methanol clusters. 34 The corrected version of this program has been applied successfully to ammonia clusters 35,36 and protonated ammonia clusters. [37][38][39] It should be noted that the free energies G n k T ð Þ can be also calculated using the module freqchk of Gaussian 16.…”

Section: Temperature Effectsmentioning

confidence: 99%

“…However, we found that acetonitrile clusters exhibits completely different structural arrangements as compared to neutral water clusters 20-22,29,61-64 and neutral ammonia clusters. 35,[65][66][67] Using the most stable structure of each cluster size, we have computed the binding energies of the neutral acetonitrile clusters (Section 3.2).…”

Section: Acetonitrile Decamer (Mecn) 10mentioning

confidence: 99%

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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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Section: Binding Energiesmentioning

confidence: 83%

Section: Temperature Effectsmentioning

confidence: 99%

Section: Acetonitrile Decamer (Mecn) 10mentioning

confidence: 99%

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Binding energies and isomer distribution of neutral acetonitrile clusters

Malloum

Fifen

Conradie

2020

Int J of Quantum Chemistry

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“…The structures of neutral and protonated ammonia clusters have completely different configurations. Small‐sized protonated ammonia clusters are dominated by branched linear and branched cyclic structures, whereas small‐sized neutral ammonia clusters favored compact structures …”

Section: Protonated Ammonia Clustersmentioning

confidence: 99%

“…Small-sized protonated ammonia clusters are dominated by branched linear and branched cyclic structures, whereas small-sized neutral ammonia clusters favored compact structures. [64,65]…”

Section: Structures Of Protonated Ammonia Clustersmentioning

confidence: 99%

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

2019

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The absolute solvation energies (free energies and enthalpies) of the proton in ammonia are used to compute the pKa of species embedded in ammonia. They are also used to compute the solvation energies of other ions in ammonia. Despite their importance, it is not possible to determine experimentally the solvation energies of the proton in a given solvent. We propose in this work a direct approach to compute the solvation energies of the proton in ammonia from large‐sized neutral and protonated ammonia clusters. To undertake this investigation, we performed a geometry optimization of neutral and protonated ammonia 30‐mer, 40‐mer, and 50 mer to locate stable structures. These structures have been fully optimized at both APFD/6‐31++g(d,p) and M06‐2X/6‐31++g(d,p) levels of theory. An infrared spectroscopic study of these structures has been provided to assess the reliability of our investigation. Using these structures, we have computed the absolute solvation free energy and the absolute solvation enthalpy of the proton in ammonia. It comes out that the absolute solvation free energy of the proton in ammonia is calculated to be −1192 kJ mol–1, whereas the absolute solvation enthalpy is evaluated to be −1214 kJ mol–1. © 2019 Wiley Periodicals, Inc.

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A Tug of War between the Self‐ and Cross‐associating Hydrogen Bonds in Neutral Ammonia‐Water Clusters: Energetic Insights by Molecular Tailoring Approach

2022

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In the present work, the energies of various types of individual HBs observed in neutral (NH3)m(H2O)n, (m+n=2 to 7) clusters were estimated using the molecular tailoring approach (MTA)‐based method. The calculated individual HB energies suggest that the O−H…N HBs are the strongest (1.21 to 12.49 kcal mol−1). The next ones are the O−H…O (3.97 to 9.30 kcal mol−1) HBs. The strengths of N−H…N (1.09 to 5.29 kcal mol−1) and N−H…O (2.85 to 5.56 kcal mol−1) HBs are the weakest. The HB energies in dimers also follow this rank ordering. However, the HB energies in dimers are much smaller than those obtained by the MTA‐based method due to the loss in cooperativity contribution in the dimers. Thus, the calculated cooperativity contributions, for different types of HBs, fall in the range 0.64 to 5.73 kcal mol−1. We wish to emphasize based on the energetic rank ordering obtained by the MTA‐based method that the O−H of water is a better HB donor than the N−H of ammonia. The reasons for the observed energetic rank ordering are two folds: (i) intrinsically stronger O−H…N HBs than the O−H…O ones as revealed by dimer energies and (ii) the higher cooperativity contribution in the former than the later ones. Indeed, the MTA‐based method is useful in providing the missing energetic rank ordering of various type of HBs in neutral (NH3)m(H2O)n clusters, in the literature.

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

Cited by 64 publications

References 77 publications

Binding energies and isomer distribution of neutral acetonitrile clusters

Binding energies and isomer distribution of neutral acetonitrile clusters

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

A Tug of War between the Self‐ and Cross‐associating Hydrogen Bonds in Neutral Ammonia‐Water Clusters: Energetic Insights by Molecular Tailoring Approach

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