Rarefied Basis Sets for the Calculation of Optical Tensors. 1. The Importance of Gradients on Hydrogen Atoms for the Raman Scattering Tensor

2004 ◽  
Vol 108 (11) ◽  
pp. 2108-2118 ◽  
Author(s):  
Gérard Zuber ◽  
Werner Hug
Keyword(s):  
Raman Scattering ◽  
Basis Sets ◽  
Hydrogen Atoms

scholarly journals A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Medium Size Molecules

2019 ◽  
Author(s):  
Pierre-Francois Loos ◽  
Filippo Lipparini ◽  
Martial Boggio-Pasqua ◽  
Anthony Scemama ◽  
Denis Jacquemin
Keyword(s):  
Oscillator Strengths ◽  
Basis Sets ◽  
Medium Size ◽  
Hydrogen Atoms ◽  
Excitation Energies ◽  
Present Contribution ◽  
Transition Energies ◽  
Vertical Excitation ◽  
Vertical Transition ◽  
Reference Space

<div><div><div><p>Following our previous work focussing on compounds containing up to 3 non-hydrogen atoms [J. Chem. Theory Comput. 14 (2018) 4360–4379], we present here highly-accurate vertical transition energies obtained for 27 molecules encompassing 4, 5, and 6 non-hydrogen atoms: acetone, acrolein, benzene, butadiene, cyanoacetylene, cyanoformaldehyde, cyanogen, cyclopentadiene, cyclopropenone, cyclopropenethione, diacetylene, furan, glyoxal, imidazole, isobutene, methylenecyclopropene, propynal, pyrazine, pyridazine, pyridine, pyrimidine, pyrrole, tetrazine, thioacetone, thiophene, thiopropynal, and triazine. To obtain these energies, we use equation-of-motion coupled cluster theory up to the highest technically possible excitation order for these systems (CC3, EOM-CCSDT, and EOM-CCSDTQ), selected configuration interaction (SCI) calculations (with tens of millions of determinants in the reference space), as well as the multiconfigurational 𝑛-electron valence state perturbation theory (NEVPT2) method. All these approaches are applied in combination with diffuse-containing atomic basis sets. For all transitions, we report at least CC3/aug-cc-pVQZ vertical excitation energies as well as CC3/aug-cc-pVTZ oscillator strengths for each dipole-allowed transition. We show that CC3 almost systematically delivers transition energies in agreement with higher-level methods with a typical deviation of ±0.04 eV, except for transitions with a dominant double excitation character where the error is much larger. The present contribution gathers a large, diverse and accurate set of more than 200 highly-accurate transition energies for states of various natures (valence, Rydberg, singlet, triplet, 𝑛 → 𝜋★, 𝜋 → 𝜋★, . . . ). We use this series of theoretical best estimates to benchmark a series of popular methods for excited state calculations: CIS(D), ADC(2), CC2, STEOM-CCSD, EOM-CCSD, CCSDR(3), CCSDT-3, CC3, as well as NEVPT2. The results of these benchmarks are compared to the available literature data.</p></div></div></div>

Kinetic Isotope and Collision Energy Effects in the Dissociation of Chloride and Bromide Adducts of Aliphatic Alcohols, Benzaldehyde, and 2,4-Pentanedione

2003 ◽  
Vol 56 (5) ◽  
pp. 415 ◽  
Author(s):  
Rodinei Augusti ◽  
Xubin Zheng ◽  
M. Turowski ◽  
R. Graham Cooks
Keyword(s):  
Density Functional ◽  
Collision Energy ◽  
Basis Set ◽  
Cluster Ions ◽  
Basis Sets ◽  
Stable Form ◽  
Triple Quadrupole Mass Spectrometer ◽  
Hydrogen Atoms ◽  
Hartree Fock ◽  
Chloride Adduct

A tandem-in-space triple quadrupole mass spectrometer was used to measure kinetic isotopic effects (KIEs) for the dissociation of chloride and bromide adducts of several compounds that bind halide anions via either hydrogen bonds or by nucleophilic attachment. Two isotopomers of each adduct were simultaneously mass-selected in the first quadrupole and dissociated by collision with argon in the second quadrupole. The KIEs were measured by comparing the extents of dissociation of the lighter versus the heavier isotopomeric adducts. In most cases, lower collision energies and multiple collision conditions favoured larger KIE values, an expected feature of easily dissociated cluster ions considering zero-point energies (ZPEs). The larger chloride adduct of cyclohexanol gave greater KIEs compared with the smaller alcohols, a consequence of slower dissociation due to the larger number of degrees of freedom. Dissociation of the chloride adducts gave greater KIEs than the corresponding bromide adducts, a result that is also consistent with expectations based on ZPEs. Both the chloride and bromide adducts of 2,4-pentanedione, when dissociated at 6 eV collision energy under single-collision conditions, displayed normal KIEs (1.0460 ± 0.0012 and 1.0092 ± 0.0035 respectively). These and the alcohol results were correctly predicted by the ZPEs calculated using commonly applied ab initio Hartree–Fock (HF) and B3LYP density functional theory (DFT) methods with large basis sets (6–311 containing both polarization and diffuse functions). Geometry optimization calculations for the 2,4-pentanedione chloride adduct using either the Restricted Hartree–Fock (RHF) method with a 6–31G* basis set or using the more accurate 6–31++G** method showed that, in the most stable form, the chloride is bonded at multiple sites by a molecule of 2,4-pentanedione. In this structure, chloride binds weakly to both the methylene and the methyl hydrogen atoms. Collision-induced dissociation furnishes chloride and 2,4-pentanedione anion ([M – H]–) as competitive negatively charged products, which is consistent with the proposed structure. It is interesting that the intermolecular KIEs in this study tend to be normal, while intramolecular isotope effects in halides, notably of the type M1Cl+M2 are inverse, as a consequence of the lower ZPEs associated with the heavier isotopomers. The difference in the two systems is that the stronger bonds are found in the products in the case of M1Cl+M2 dissociation but in the reactants in the case of MCl– dissociation.

HYDROGEN SULFIDE STABILIZATION OF AN EXCESS ELECTRON ON MOLECULAR SURFACES

2008 ◽  
Vol 07 (01) ◽  
pp. 157-166 ◽  
Author(s):  
ABRAHAM F. JALBOUT
Keyword(s):  
Hydrogen Sulfide ◽  
Dipole Moment ◽  
Bound States ◽  
Positive Charge ◽  
Basis Sets ◽  
Electron Detachment ◽  
Hydrogen Atoms ◽  
Molecular Surfaces ◽  
Oh Groups ◽  
Excess Electrons

In the present work, a set of cyclooctane and cyclohexane molecular surfaces were used to solvate excess electrons using hydrogen sulfide ( H 2 S ). The compounds implemented have been constructed with OH groups on one side of the hydrocarbon surfaces and hydrogen atoms on the opposite side. These OH groups increased the dipole moment of systems. Simultaneously the hydrogen atoms on the opposite side of the surface for a pocket of positive charge that can attach excess electrons via dipole-bound states. The solvated anions formed between the molecular surfaces and hydrogen sulfide are stable with respect to vertical electron detachment (VDE). The effect of basis sets was also addressed in the context of VDE calculations.

Basis set dependence using DFT/B3LYP calculations to model the Raman spectrum of thymine

2016 ◽  
Vol 14 (01) ◽  
pp. 1650002 ◽  
Author(s):  
Jakub Bielecki ◽  
Ewelina Lipiec
Keyword(s):  
Raman Spectroscopy ◽  
Ionizing Radiation ◽  
Raman Spectra ◽  
Density Functional ◽  
Surface Enhanced Raman Spectroscopy ◽  
Basis Set ◽  
Basis Sets ◽  
Hydrogen Atoms ◽  
Additional Layer ◽  
Tip Enhanced Raman Spectroscopy

Raman spectroscopy (including surface enhanced Raman spectroscopy (SERS) and tip enhanced Raman spectroscopy (TERS)) is a highly promising experimental method for investigations of biomolecule damage induced by ionizing radiation. However, proper interpretation of changes in experimental spectra for complex systems is often difficult or impossible, thus Raman spectra calculations based on density functional theory (DFT) provide an invaluable tool as an additional layer of understanding of underlying processes. There are many works that address the problem of basis set dependence for energy and bond length consideration, nevertheless there is still lack of consistent research on basis set influence on Raman spectra intensities for biomolecules. This study fills this gap by investigating of the influence of basis set choice for the interpretation of Raman spectra of the thymine molecule calculated using the DFT/B3LYP framework and comparing these results with experimental spectra. Among 19 selected Pople’s basis sets, the best agreement was achieved using 6-31[Formula: see text](d,p), 6-31[Formula: see text](d,p) and 6-11[Formula: see text]G(d,p) sets. Adding diffuse functions or polarized functions for small basis set or use of a medium or large basis set without diffuse or polarized functions is not sufficient to reproduce Raman intensities correctly. The introduction of the diffuse functions ([Formula: see text]) on hydrogen atoms is not necessary for gas phase calculations. This work serves as a benchmark for further research on the interaction of ionizing radiation with DNA molecules by means of ab initio calculations and Raman spectroscopy. Moreover, this work provides a set of new scaling factors for Raman spectra calculation in the framework of DFT/B3LYP method.

scholarly journals Crystal structure of new formamidinium triiodide jointly refined by single-crystal XRD, Raman scattering spectroscopy and DFT assessment of hydrogen-bond network features

2021 ◽  
Vol 77 (7) ◽  
pp. 692-695
Author(s):  
Artem A. Ordinartsev ◽  
Andrey A. Petrov ◽  
Konstantin A. Lyssenko ◽  
Andrey V. Petrov ◽  
Eugene A. Goodilin ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Raman Scattering ◽  
Population Analysis ◽  
Hydrogen Atoms ◽  
Mulliken Population ◽  
Triclinic Space Group ◽  
Raman Scattering Spectroscopy ◽  
Scattering Spectra ◽  
Bond Network ◽  
Raman Scattering Spectra

A novel triiodide phase of the formamidinium cation, CH5N2 +·I3 −, crystallizes in the triclinic space group P\overline{1} at a temperature of 110 K. The structure consists of two independent isolated triiodide ions located on inversion centers. The centrosymmetric character of I3 − was additionally confirmed by the observed pronounced peaks of symmetrical oscillations of I3 − at 115–116 cm−1 in Raman scattering spectra. An additional structural feature is that each terminal iodine atom is connected with three neighboring planar formamidinium cations by N—H...I hydrogen bonding with the N—H...I bond length varying from 2.81 to 3.08 Å, forming a deformed two-dimensional framework of hydrogen bonds. A Mulliken population analysis showed that the calculated charges of hydrogen atoms correlate well with hydrogen-bond lengths. The crystal studied was refined as a three-component twin with domain ratios of 0.631 (1):0.211 (1):0.158 (1).

scholarly journals A Mountaineering Strategy to Excited States: Highly-Accurate Energies and Benchmarks for Medium Size Molecules

2019 ◽  
Author(s):  
Pierre-Francois Loos ◽  
Filippo Lipparini ◽  
Martial Boggio-Pasqua ◽  
Anthony Scemama ◽  
Denis Jacquemin
Keyword(s):  
Oscillator Strengths ◽  
Basis Sets ◽  
Medium Size ◽  
Hydrogen Atoms ◽  
Excitation Energies ◽  
Present Contribution ◽  
Transition Energies ◽  
Vertical Excitation ◽  
Vertical Transition ◽  
Reference Space

<div><div><div><p>Following our previous work focussing on compounds containing up to 3 non-hydrogen atoms [J. Chem. Theory Comput. 14 (2018) 4360–4379], we present here highly-accurate vertical transition energies obtained for 27 molecules encompassing 4, 5, and 6 non-hydrogen atoms: acetone, acrolein, benzene, butadiene, cyanoacetylene, cyanoformaldehyde, cyanogen, cyclopentadiene, cyclopropenone, cyclopropenethione, diacetylene, furan, glyoxal, imidazole, isobutene, methylenecyclopropene, propynal, pyrazine, pyridazine, pyridine, pyrimidine, pyrrole, tetrazine, thioacetone, thiophene, thiopropynal, and triazine. To obtain these energies, we use equation-of-motion coupled cluster theory up to the highest technically possible excitation order for these systems (CC3, EOM-CCSDT, and EOM-CCSDTQ), selected configuration interaction (SCI) calculations (with tens of millions of determinants in the reference space), as well as the multiconfigurational 𝑛-electron valence state perturbation theory (NEVPT2) method. All these approaches are applied in combination with diffuse-containing atomic basis sets. For all transitions, we report at least CC3/aug-cc-pVQZ vertical excitation energies as well as CC3/aug-cc-pVTZ oscillator strengths for each dipole-allowed transition. We show that CC3 almost systematically delivers transition energies in agreement with higher-level methods with a typical deviation of ±0.04 eV, except for transitions with a dominant double excitation character where the error is much larger. The present contribution gathers a large, diverse and accurate set of more than 200 highly-accurate transition energies for states of various natures (valence, Rydberg, singlet, triplet, 𝑛 → 𝜋★, 𝜋 → 𝜋★, . . . ). We use this series of theoretical best estimates to benchmark a series of popular methods for excited state calculations: CIS(D), ADC(2), CC2, STEOM-CCSD, EOM-CCSD, CCSDR(3), CCSDT-3, CC3, as well as NEVPT2. The results of these benchmarks are compared to the available literature data.</p></div></div></div>

scholarly journals Calculation of VS,max and Its Use as a Descriptor for the Theoretical Calculation of pKa Values for Carboxylic Acids

Molecules ◽  
2018 ◽  
Vol 24 (1) ◽  
pp. 79 ◽  
Author(s):  
Guillermo Caballero-García ◽  
Gustavo Mondragón-Solórzano ◽  
Raúl Torres-Cadena ◽  
Marco Díaz-García ◽  
Jacinto Sandoval-Lira ◽  
...  
Keyword(s):  
Theoretical Calculation ◽  
Carboxylic Acids ◽  
Predictive Power ◽  
Basis Sets ◽  
Hydrogen Atoms ◽  
Pka Values ◽  
Implicit Solvation Model ◽  
Moller Plesset ◽  
Surface Electrostatic Potential ◽  
Acidic Hydrogen

The theoretical calculation of pKa values for Brønsted acids is a challenging task that involves sophisticated and time-consuming methods. Therefore, heuristic approaches are efficient and appealing methodologies to approximate these values. Herein, we used the maximum surface electrostatic potential (VS,max) on the acidic hydrogen atoms of carboxylic acids to describe the H-bond interaction with water (the same descriptor that is used to characterize σ-bonded complexes) and correlate the results with experimental pKa values to obtain a predictive model for other carboxylic acids. We benchmarked six different methods, all including an implicit solvation model (water): Five density functionals and the Møller–Plesset second order perturbation theory in combination with six different basis sets for a total of thirty-six levels of theory. The ωB97X-D/cc-pVDZ level of theory stood out as the best one for consistently reproducing the reported pKa values, with a predictive power of 98% correlation in a test set of ten other carboxylic acids.

CALCULATIONS AND EXPERIMENTAL STUDIES OF THE AGGREGATION OF MOLECULES OF LIQUID ACETONE BY SPECTRA OF RAMAN SCATTERING

2013 ◽  
Vol 22 (02) ◽  
pp. 1350022 ◽  
Author(s):  
F. H. TUKHVATULLIN ◽  
U. N. TASHKENBAEV ◽  
A. JUMABAEV ◽  
H. HUSHVAKTOV ◽  
A. ABSANOV ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Oxygen Atom ◽  
Raman Scattering ◽  
Experimental Studies ◽  
Energy Gain ◽  
Half Width ◽  
Hydrogen Atoms ◽  
Aqueous Mixture ◽  
The Difference ◽  
Liquid Acetone

Experimental studies of the Raman scattering of the band of C = O vibrations of acetone (1710 cm–1) showed that the parallel and perpendicular polarized components have a large half-width (respectively, 11.6 and 18 cm–1) and also the bands' maxima of these components are shifted by ~5 cm–1. In the neutral solvent (heptane), the difference of the maxima position of the bands decreases. Calculations showed that the molecules of acetone can aggregate to form a dimer with the energy gain of 10.1 kJ/mole. In the dimer several hydrogen bonds are formed between the oxygen atom of one molecule and the hydrogen atoms of CH3 -group of another molecule. In an aqueous mixture of acetone, according to calculations, there is a possibility for formation of dimers and closed trimer aggregates with the energy gain, respectively, 19.1 and 45.8 kJ/mole. Calculation showed that symmetric and antisymmetric O–H vibrations of water are displaced in the interaction with acetone to lower frequencies, respectively, to 3808.4 and to 3931.8 –1.

Ab initio Studies on Hydrazines: 2H-1,2,3-Triazol-2-amine With Special Reference to Its Equilibrium Structure and Vibrational Spectrum

1989 ◽  
Vol 42 (3) ◽  
pp. 433 ◽  
Author(s):  
NV Riggs
Keyword(s):  
Hydrogen Bonding ◽  
Vibrational Energy ◽  
Zero Point ◽  
Equilibrium Structure ◽  
Basis Sets ◽  
Transition Structure ◽  
Hydrogen Atoms ◽  
Ring Nitrogen ◽  
Experimental Values ◽  
Double Hydrogen

The geometries of four stationary structures of 2H-1,2,3-triazol-2-amine have been optimized with the 3-21G and 3-21G(N*) basis sets. The lowest-energy and only equilibrium structure predicted by these calculations is the 'perpendicular' Cs form (3), whereas infrared studies on benzo-annelated analogues had suggested it might be the 'parallel' Cs form (2) stabilized by 'double hydrogen-bonding' of the amino-hydrogen atoms to the flanking ring-nitrogen atoms. The latter form (2) is here characterized as the transition structure for rotation about the N-NH2 bond and, after zero-point vibrational-energy corrections, is calculated to lie 8.7 kJ mol-1 above the equilibrium structure (3) at HF/3-21G(N*) level or only 3.8 kJ mol-1 at MP4/6-31G** level. This very low barrier to internal rotation (cf. 26.5 kJ mol-1 for the analogous 1H-pyrrol-1-amine) may be due to double hydrogen-bonding of the kind suggested by the experimental study mentioned above. The transition structure for inversion at the NH2 centre is, as for 1H-pyrrol-1-amine, the perpendicular C2v structure (5), the barrier being 25.8 kJ mol-1 (cf. 24.5 kJ mol-1 for 1H-pyrrol-1-amine), and the planar C2v structure (4) is a second-order saddle point lying 41.7 kJ mol-1 above the equilibrium structure (3). Calculated NH-stretching frequencies, their separation, and relative intensities as compared with experimental values for benzo-annelated analogues offer broad support for the assignments above based on relative energies.

A Computational Study on Structural and Electronic Properties of 1-(4-Chlorophenyl)-2-{[5-(4-Chlorophenyl)-1,2,3-Oxadiazol-2-Yl]Sulfanyl}Ethanone

2019 ◽  
Vol 892 ◽  
pp. 1-7
Author(s):  
Pek Lan Toh ◽  
Montha Meepripruk ◽  
Rosfayanti Rasmidi
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Molecular System ◽  
Population Analysis ◽  
Atomic Charge ◽  
Dft Method ◽  
Basis Sets ◽  
Hydrogen Atoms ◽  
Mulliken Population ◽  
Total Energies

In this paper, a first principle Density Functional Theory (DFT) method was conducted to study the geometric and electronic structures of 1-(4-chlorophenyl)-2-{[5-(4-chlorophenyl) -1,3,4-oxadiazol-2-yl] sulfanyl} ethanone, C16H10Cl2N2O2S. Using B3LYP level of theory with four basis sets of 6-31G**, 6-31++G**, 6-311G**, and 6-311++G**, the equilibrium structure of the title molecule was used to determine the total energies, Frontier molecular orbital’s energies, Mulliken atomic charges, and others. The computed findings present that four total energies obtained are close to each other, with the corresponding values of-59716.06 eV, -59709.42 eV, -59708.56 eV, and-59716.51 eV, respectively for B3LYP/6-31G**, B3LYP/6-31++G**, B3LYP/6-311G**, and B3LYP/6-311++G** methods. The calculated HOMO-LUMO energy gaps were predicted in the range of 4.001 eV - 4.089 eV. In this study, the atomic charge values of molecular system were also determined using Mulliken Population Analysis (MPA) approach. For DFT/B3LYP/6-311G** level of calculation, the computed results show that the atom of C8 accommodates the highest negative charge in the title molecular system. All the oxygen, nitrogen, and chloride atoms are having negative charges, whereas all the hydrogen atoms are having positive charges. In addition, the dipole moment value was also determined to be 1.4758 Debye by employing DFT/B3LYP/6-311G** level of theory.

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