scholarly journals BSE49, a diverse, high-quality benchmark dataset of separation energies of chemical bonds

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Viki Kumar Prasad ◽  
M. Hossein Khalilian ◽  
Alberto Otero-de-la-Roza ◽  
Gino A. DiLabio
Keyword(s):  
Experimental Data ◽  
State Energy ◽  
Zero Point ◽  
Reference Dataset ◽  
High Quality ◽  
Point Energy ◽  
Covalently Bonded ◽  
Model Structures ◽  
Cl Atoms ◽  
Single Bonds

AbstractWe present an extensive and diverse dataset of bond separation energies associated with the homolytic cleavage of covalently bonded molecules (A-B) into their corresponding radical fragments (A. and B.). Our dataset contains two different classifications of model structures referred to as “Existing” (molecules with associated experimental data) and “Hypothetical” (molecules with no associated experimental data). In total, the dataset consists of 4502 datapoints (1969 datapoints from the Existing and 2533 datapoints from the Hypothetical classes). The dataset covers 49 unique X-Y type single bonds (except H-H, H-F, and H-Cl), where X and Y are H, B, C, N, O, F, Si, P, S, and Cl atoms. All the reference data was calculated at the (RO)CBS-QB3 level of theory. The reference bond separation energies are non-relativistic ground-state energy differences and contain no zero-point energy corrections. This new dataset of bond separation energies (BSE49) is presented as a high-quality reference dataset for assessing and developing computational chemistry methods.

Thermodynamic properties and melting of solid helium

1953 ◽  
Vol 218 (1134) ◽  
pp. 291-310 ◽  
Keyword(s):  
Experimental Data ◽  
Solid Helium ◽  
Characteristic Temperature ◽  
Melting Curve ◽  
Zero Point ◽  
Point Energy ◽  
Melting Temperatures ◽  
Wide Range ◽  
Melting Properties ◽  
The Difference

The melting properties and thermodynamic functions of solid helium have been determined at temperatures from 4 to 26° K and at pressures up to 3000 atm. The upper temperature corresponds to about five times the critical temperature of helium; it was therefore possible to measure properties of the solid state in a range which has not yet been attained for any other substance. The melting curve shows no signs of an approach to a solid-fluid critical point; in fact, the difference between the phases becomes more pronounced at higher melting temperatures. The internal energy at 0° K was calculated from the experimental data and was found to be in good agreement with the theoretical values based on the Slater-Kirkwood potential, using 9/8 Rθ as an estimate of the zero-point energy ( θ being the Debye characteristic temperature). A first-order transition in the solid was revealed; its equilibrium line cuts the melting curve at 14.9° K and moves to higher temperatures at higher densities. The heat of transition is very small, about 0.08 cal/mole. The transition is assumed to correspond to a change of crystal structure from hexagonal to cubic close-packed. At the highest pressure solid helium is compressed to less than half its volume under equilibrium conditions at absolute zero, and the Debye θ is increased five times. It was hence possible to test the Lindemann melting formula for a single substance over a very wide range. The formula was found to fit the experimental data satisfactorily, although the value of the constant in it differed somewhat from the classical value.

scholarly journals Dispersion of Phonons in Ideal Crystals

1969 ◽  
Vol 22 (4) ◽  
pp. 471 ◽  
Author(s):  
NP Gupta
Keyword(s):  
Experimental Data ◽  
Phonon Dispersion ◽  
Zero Point ◽  
Lattice Vibrations ◽  
Rare Gases ◽  
Point Energy ◽  
Phonon Dispersion Curves ◽  
Debye Theory ◽  
Specific Heats ◽  
Theoretical Frequency

A quasiharmonic central force rigid-atom model has been used to study the lattice vibrations of frozen rare gases. The model takes care of interactions up to fourth neighbour and estimates zero-point energy and its volume derivatives by the Debye theory of specific heats. The theoretical frequency distribution and phonon dispersion curves are found to compare reasonably well with the available experimental data. Various causes of the discrepancies and possibilities of improvement of the results are discussed.

Analysis and reporting recommendations for theoretical and experimental ionization potentials based on the study of 53 medium sized molecules using the IP-EOMCCSD method.

2019 ◽  
Author(s):  
Marissa Buzzanca ◽  
Brandon Brummeyer ◽  
Jonathan Gutow
Keyword(s):  
Experimental Data ◽  
Zero Point ◽  
Ionization Potentials ◽  
Basis Set ◽  
Zero Point Energy ◽  
Point Energy ◽  
Complete Basis ◽  
Complete Basis Set ◽  
Vertical Ionization Potentials ◽  
Theory And Experiment

<div> <div> <div>The precision and accuracy of theoretical vertical ionization potential calculations has improved to the point where more care is needed to make valid comparisons with experimental measurements then is currently the norm. Vertical ionization potentials (IPs) computed using the IP-EOMCCSD method are reported for 53 medium sized molecules (6 – 32 atoms) and compared with statistically evaluated experimental vertical IPs. Based on this comparison, theoretical IPs should be extrapolated to the complete basis set limit and corrected for vibrational zero-point energy, while for experimental data the intensity weighted mean band position should be reported as the vertical IP. Experimental data available for ethylene, E-2-butene, 2,5-dihydrofuran and pyrrole were re-analyzed and compared with zero-point energy corrected complete basis set theoretical estimates, yielding an average discrepancy of 0.05 eV between theory and experiment. In contrast the average of reported experimental vertical IPs (the comparison usually made) yielded an average discrepancy of 0.25 eV between theory and experiment for these molecules. Further analysis of the remaining molecules in the data set suggests that the majority of reported experimental vertical IPs are low because band asymmetries were not accounted for when assigning IP values. This leads to fortuitous good agreement between experiment and computations using the smaller aug-cc-pVDZ basis set without zero-point correction. In the case of 1,4-cyclohexadiene there is strong evidence for experimental uncertainty accounting for the discrepency between theory and experiment. The presented results provide a benchmark for evaluating both experimental and theoretical estimates of vertical ionization potentials for the 53 molecules studied. </div> </div> </div>

Analysis and reporting recommendations for theoretical and experimental ionization potentials based on the study of 53 medium sized molecules using the IP-EOMCCSD method.

2019 ◽  
Author(s):  
Marissa Buzzanca ◽  
Brandon Brummeyer ◽  
Jonathan Gutow
Keyword(s):  
Experimental Data ◽  
Zero Point ◽  
Ionization Potentials ◽  
Basis Set ◽  
Zero Point Energy ◽  
Point Energy ◽  
Complete Basis ◽  
Complete Basis Set ◽  
Vertical Ionization Potentials ◽  
Theory And Experiment

<div> <div> <div>The precision and accuracy of theoretical vertical ionization potential calculations has improved to the point where more care is needed to make valid comparisons with experimental measurements then is currently the norm. Vertical ionization potentials (IPs) computed using the IP-EOMCCSD method are reported for 53 medium sized molecules (6 – 32 atoms) and compared with statistically evaluated experimental vertical IPs. Based on this comparison, theoretical IPs should be extrapolated to the complete basis set limit and corrected for vibrational zero-point energy, while for experimental data the intensity weighted mean band position should be reported as the vertical IP. Experimental data available for ethylene, E-2-butene, 2,5-dihydrofuran and pyrrole were re-analyzed and compared with zero-point energy corrected complete basis set theoretical estimates, yielding an average discrepancy of 0.05 eV between theory and experiment. In contrast the average of reported experimental vertical IPs (the comparison usually made) yielded an average discrepancy of 0.25 eV between theory and experiment for these molecules. Further analysis of the remaining molecules in the data set suggests that the majority of reported experimental vertical IPs are low because band asymmetries were not accounted for when assigning IP values. This leads to fortuitous good agreement between experiment and computations using the smaller aug-cc-pVDZ basis set without zero-point correction. In the case of 1,4-cyclohexadiene there is strong evidence for experimental uncertainty accounting for the discrepency between theory and experiment. The presented results provide a benchmark for evaluating both experimental and theoretical estimates of vertical ionization potentials for the 53 molecules studied. </div> </div> </div>

Discrete lattice model for the large polaron

1991 ◽  
Vol 69 (5) ◽  
pp. 635-640 ◽  
Author(s):  
V. V. Paranjape ◽  
P. V. Panat
Keyword(s):  
Ground State ◽  
Weak Coupling ◽  
State Energy ◽  
Zero Point ◽  
Weak Coupling Limit ◽  
Point Energy ◽  
Model Based ◽  
Discrete Nature ◽  
Polaron Energy ◽  
Polaron Radius

The energy states of a polaron in the weak-coupling limit were first obtained by Fröhlich and co-workers, assuming that the polarization of the lattice due to the electron is continuous. If the polaron radius is comparable to the lattice constant then the assumption is inappropriate. A model based on the discrete nature of the lattice is more suitable. Such a model, based on the semiclassical zero-point energy, is proposed. We have calculated the ground-state energy of the polaron and the energy of the polaron near the bottom of the conduction band. The first discussion of the effect of lattice discreteness on the polaron energy was presented by Lepine and Frongillo who used for their calculations, a method based on the "kq" representation. Our method differs from the method of these earlier authors but the results of the two approaches are similar. Some differences exist nevertheless. The main aim of this paper is, therefore, to provide an alternate method for calculating the effect of discreteness on the polaron energy. The differences arising between the results of the two methods are discussed.

On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulations

2019 ◽  
Author(s):  
Riccardo Spezia ◽  
Hichem Dammak
Keyword(s):  
Degrees Of Freedom ◽  
Molecular Simulations ◽  
Zero Point ◽  
Thermal Bath ◽  
Unimolecular Dissociation ◽  
Point Energy ◽  
Rotational Degrees Of Freedom ◽  
The Difference ◽  
Nuclear Effects

<div> <div> <div> <p>In the present work we have investigated the possibility of using the Quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is aimed in introducing quantum nuclear effects with a com- putational time which is basically the same as in newtonian simulations. At this end we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model a microcanonical algorithm which monitor zero-point energy of products, and eventually modifies tra- jectories, was recently proposed. We have thus compared classical and quantum rate constant with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study unimolecular fragmentation of much complex systems with molecular simulations. The role of QTB thermostat on rotational degrees of freedom is also analyzed and discussed. </p> </div> </div> </div>

scholarly journals Modulation of optical absorption in m-Fe1−xRuxS2 and exploring stability in new m-RuS2

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
H. Joshi ◽  
M. Ram ◽  
N. Limbu ◽  
D. P. Rai ◽  
B. Thapa ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Phonon Dispersion ◽  
Applied Pressure ◽  
Orthorhombic Phase ◽  
Zero Point ◽  
Computational Method ◽  
Crystal Field Theory ◽  
Point Energy ◽  
Practical Applications ◽  
New Phase

AbstractA first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. In addition, we have also revealed a new marcasite phase in RuS2, unlike most studied pyrite structures. The new phase has fulfilled all the necessary criteria of structural stability and its practical existence. The transition pressure of 8 GPa drives the structural change from pyrite to orthorhombic phase in RuS2. From the thermodynamical calculation, we have reported the stability of new-phase under various ranges of applied pressure and temperature. Further, from the results of phonon dispersion calculated at Zero Point Energy, pyrite structure exhibits ground state stability and the marcasite phase has all modes of frequencies positive. The newly proposed phase is a semiconductor with a band gap comparable to its pyrite counterpart but vary in optical absorption by around 106 cm−1. The various Ru doped structures have also shown similar optical absorption spectra in the same order of magnitude. We have used crystal field theory to explain high optical absorption which is due to the involvement of different electronic states in formation of electronic and optical band gaps. Lӧwdin charge analysis is used over the customarily Mulliken charges to predict 89% of covalence in the compound. Our results indicate the importance of new phase to enhance the efficiency of photovoltaic materials for practical applications.

scholarly journals Dynamical strengthening of covalent and non-covalent molecular interactions by nuclear quantum effects at finite temperature

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Huziel E. Sauceda ◽  
Valentin Vassilev-Galindo ◽  
Stefan Chmiela ◽  
Klaus-Robert Müller ◽  
Alexandre Tkatchenko
Keyword(s):  
Finite Temperature ◽  
Electrostatic Interactions ◽  
Zero Point ◽  
Quantum Effects ◽  
Van Der Waals Interactions ◽  
Interatomic Distances ◽  
Point Energy ◽  
Molecular Bond ◽  
Energy Surfaces ◽  
Nuclear Quantum Effects

AbstractNuclear quantum effects (NQE) tend to generate delocalized molecular dynamics due to the inclusion of the zero point energy and its coupling with the anharmonicities in interatomic interactions. Here, we present evidence that NQE often enhance electronic interactions and, in turn, can result in dynamical molecular stabilization at finite temperature. The underlying physical mechanism promoted by NQE depends on the particular interaction under consideration. First, the effective reduction of interatomic distances between functional groups within a molecule can enhance the n → π* interaction by increasing the overlap between molecular orbitals or by strengthening electrostatic interactions between neighboring charge densities. Second, NQE can localize methyl rotors by temporarily changing molecular bond orders and leading to the emergence of localized transient rotor states. Third, for noncovalent van der Waals interactions the strengthening comes from the increase of the polarizability given the expanded average interatomic distances induced by NQE. The implications of these boosted interactions include counterintuitive hydroxyl–hydroxyl bonding, hindered methyl rotor dynamics, and molecular stiffening which generates smoother free-energy surfaces. Our findings yield new insights into the versatile role of nuclear quantum fluctuations in molecules and materials.

scholarly journals Time-Resolved Measurements and Master Equation Modelling of the Unimolecular Decomposition of CH3OCH2

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1233-1250 ◽  
Author(s):  
Arrke J. Eskola ◽  
Mark A. Blitz ◽  
Michael J. Pilling ◽  
Paul W. Seakins ◽  
Robin J. Shannon
Keyword(s):  
Energy Transfer ◽  
Master Equation ◽  
Rate Coefficient ◽  
Zero Point ◽  
Buffer Gas ◽  
Unimolecular Decomposition ◽  
Time Resolved ◽  
Point Energy ◽  
Wide Range ◽  
Transfer Parameters

AbstractThe rate coefficient for the unimolecular decomposition of CH3OCH2, k1, has been measured in time-resolved experiments by monitoring the HCHO product. CH3OCH2 was rapidly and cleanly generated by 248 nm excimer photolysis of oxalyl chloride, (ClCO)2, in an excess of CH3OCH3, and an excimer pumped dye laser tuned to 353.16 nm was used to probe HCHO via laser induced fluorescence. k1(T,p) was measured over the ranges: 573–673 K and 0.1–4.3 × 1018 molecule cm−3 with a helium bath gas. In addition, some experiments were carried out with nitrogen as the bath gas. Ab initio calculations on CH3OCH2 decomposition were carried out and a transition-state for decomposition to CH3 and H2CO was identified. This information was used in a master equation rate calculation, using the MESMER code, where the zero-point-energy corrected barrier to reaction, ΔE0,1, and the energy transfer parameters, ⟨ΔEdown⟩ × Tn, were the adjusted parameters to best fit the experimental data, with helium as the buffer gas. The data were combined with earlier measurements by Loucks and Laidler (Can J. Chem.1967, 45, 2767), with dimethyl ether as the third body, reinterpreted using current literature for the rate coefficient for recombination of CH3OCH2. This analysis returned ΔE0,1 = (112.3 ± 0.6) kJ mol−1, and leads to $k_{1}^{\infty}(T)=2.9\times{10^{12}}$ (T/300)2.5 exp(−106.8 kJ mol−1/RT). Using this model, limited experiments with nitrogen as the bath gas allowed N2 energy transfer parameters to be identified and then further MESMER simulations were carried out, where N2 was the buffer gas, to generate k1(T,p) over a wide range of conditions: 300–1000 K and N2 = 1012–1025 molecule cm−3. The resulting k1(T,p) has been parameterized using a Troe-expression, so that they can be readily be incorporated into combustion models. In addition, k1(T,p) has been parametrized using PLOG for the buffer gases, He, CH3OCH3 and N2.

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