TiCl, TiH, and TiH + bond energies: a test of a correlation-consistent Ti basis set

1999 ◽  
Vol 103 (2) ◽  
pp. 141-145 ◽  
Author(s):  
Charles W. Bauschlicher Jr
Keyword(s):  
Basis Set ◽  
Bond Energies ◽  
Correlation Consistent

scholarly journals Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes

Molecules ◽  
2021 ◽  
Vol 26 (8) ◽  
pp. 2310
Author(s):  
Nathan C. Frey ◽  
Eric Van Dornshuld ◽  
Charles Edwin Webster
Keyword(s):  
Transition Metals ◽  
Density Functional ◽  
Chemical Shifts ◽  
Transition States ◽  
Electronic Energy ◽  
Basis Set ◽  
Composite Approach ◽  
Temperature Regimes ◽  
Correlation Consistent Composite Approach ◽  
Correlation Consistent

The correlation consistent Composite Approach for transition metals (ccCA-TM) and density functional theory (DFT) computations have been applied to investigate the fluxional mechanisms of cyclooctatetraene tricarbonyl chromium ((COT)Cr(CO)3) and 1,3,5,7-tetramethylcyclooctatetraene tricarbonyl chromium, molybdenum, and tungsten ((TMCOT)M(CO)3 (M = Cr, Mo, and W)) complexes. The geometries of (COT)Cr(CO)3 were fully characterized with the PBEPBE, PBE0, B3LYP, and B97-1 functionals with various basis set/ECP combinations, while all investigated (TMCOT)M(CO)3 complexes were fully characterized with the PBEPBE, PBE0, and B3LYP methods. The energetics of the fluxional dynamics of (COT)Cr(CO)3 were examined using the correlation consistent Composite Approach for transition metals (ccCA-TM) to provide reliable energy benchmarks for corresponding DFT results. The PBE0/BS1 results are in semiquantitative agreement with the ccCA-TM results. Various transition states were identified for the fluxional processes of (COT)Cr(CO)3. The PBEPBE/BS1 energetics indicate that the 1,2-shift is the lowest energy fluxional process, while the B3LYP/BS1 energetics (where BS1 = H, C, O: 6-31G(d′); M: mod-LANL2DZ(f)-ECP) indicate the 1,3-shift having a lower electronic energy of activation than the 1,2-shift by 2.9 kcal mol−1. Notably, PBE0/BS1 describes the (CO)3 rotation to be the lowest energy process, followed by the 1,3-shift. Six transition states have been identified in the fluxional processes of each of the (TMCOT)M(CO)3 complexes (except for (TMCOT)W(CO)3), two of which are 1,2-shift transition states. The lowest-energy fluxional process of each (TMCOT)M(CO)3 complex (computed with the PBE0 functional) has a ΔG‡ of 12.6, 12.8, and 13.2 kcal mol−1 for Cr, Mo, and W complexes, respectively. Good agreement was observed between the experimental and computed 1H-NMR and 13C-NMR chemical shifts for (TMCOT)Cr(CO)3 and (TMCOT)Mo(CO)3 at three different temperature regimes, with coalescence of chemically equivalent groups at higher temperatures.

Spectroscopic investigations on BH+ (X2 Σ+ ) ion using MRCI method and correlation-consistent sextuple basis set augmented with diffuse functions

2011 ◽  
Vol 111 (10) ◽  
pp. 2171-2179 ◽  
Author(s):  
De-Heng Shi ◽  
Hui Liu ◽  
Jin-Ping Zhang ◽  
Jin-Feng Sun ◽  
Yu-Fang Liu ◽  
...  
Keyword(s):  
Basis Set ◽  
Spectroscopic Investigations ◽  
Correlation Consistent

Inelastic scattering of interstellar silyl cyanide (SiH3CN) by helium atoms : cross-sections and rate coefficients for A- and E-SiH3CN

2021 ◽  
Vol 507 (4) ◽  
pp. 5264-5271
Author(s):  
Manel Naouai ◽  
Abdelhak Jrad ◽  
Ayda Badri ◽  
Faouzi Najar
Keyword(s):  
Inelastic Scattering ◽  
Total Energy ◽  
Cross Sections ◽  
Three Dimensional ◽  
Basis Set ◽  
Rate Coefficients ◽  
Close Coupling ◽  
Explicitly Correlated ◽  
Correlation Consistent ◽  
Triple Excitation

ABSTRACT Rotational inelastic scattering of silyl cyanide (SiH3CN) molecule with helium (He) atoms is investigated. Three-dimensional potential energy surface (3D-PES) for the SiH3CN–He interacting system is carried out. The ab initio 3D-PES is computed using explicitly correlated coupled cluster approach with single, double, and perturbative triple excitation CCSD(T)-F12a connected to augmented-correlation consistent-polarized valence triple zeta Gaussian basis set. A global minimum at (R = 6.35 bohr; θ = 90○; ϕ = 60○) with a well depth of 52.99 cm−1 is pointed out. Inelastic rotational cross-sections are emphasized for the 22 first rotational levels for total energy up to 500 cm−1 via close coupling (CC) approach in the case of A-SiH3CN and for the 24 first rotational levels for total energy up to 100 cm−1 via CC and from 100 to 500 cm−1 via coupled states (CS) in the case of E-SiH3CN. Rate coefficients are derived for temperature until 80 K for both A- and E-SiH3CN–He systems. Propensity rules are obtained for |ΔJ| = 2 processes with broken parity for A-SiH3CN and for |ΔJ| = 2 processes with |ΔK| = 0 and unbroken parity for E-SiH3CN.

Semiclassical model calculations of weak, strong, and short H-bonds

1991 ◽  
Vol 69 (11) ◽  
pp. 1819-1826 ◽  
Author(s):  
Werner A. P. Luck ◽  
Thomas Wess
Keyword(s):  
Integral Method ◽  
Basis Set ◽  
Bond Energies ◽  
Model Calculations ◽  
Semiclassical Model ◽  
Phase Integral ◽  
Simple Phase ◽  
Tunnel Effects ◽  
Isotopic Effects ◽  
Ubbelohde Effect

The OH potentials of the complexes [Formula: see text] are calculated by an ab initio MO-LCAO-SCF-CISD method with a 6-31G** basis set for 30 different [Formula: see text] distances. The resulting OH vibration levels are calculated by the so-called semiclassical Planck–Sommerfeld phase integral. The experimental H-bond effects on vibration spectra, and their anomalies, could be established by calculations of H-bond energies, OH frequencies, anharmonicities, the Badger–Bauer rule, correlation between OH and [Formula: see text] distances, isotopic effects, and the Ubbelohde effect. For very short H-bonds new properties could be predicted. There seem to exist three classes of H-bond: (1) weak or medium-strong, (2) strong, and (3) very short. The simple phase integral method could demonstrate the anomalous effects of strong H-bonds solely by the transition from two separated minima to one, without necessarily assuming tunnel effects. Key words: strong H-bonds, IR spectra and theory, tunnel effects.

scholarly journals Ab initio study of the mechanism of the reaction ClO + O --> Cl + O2

2021 ◽  
Vol 66 (1) ◽  
Author(s):  
S. Naskar ◽  
G. Nandi ◽  
T. K. Ghosh
Keyword(s):  
Reaction Mechanism ◽  
Ab Initio ◽  
Minimum Energy ◽  
Transition States ◽  
Basis Set ◽  
Heat Of Reaction ◽  
Minimal Basis ◽  
Dissociation Energies ◽  
Correlation Consistent ◽  
Equilibrium Geometries

Abstract. Ab initio investigation on the reaction mechanism of ClO + O --> Cl + O2 reaction has been performed using correlation consistent triple zeta basis set. The geometry and frequency of the reactants, products, minimum energy geometries and transition states are obtained using MP2 method and energetics are obtained at the QCISD(T)//MP2 level of theory. Primarily, a possible reaction mechanism is obtained on the basis on IRC calculations using MP2 level of theory. To obtain true picture of the reaction path, we performed IRC calculations using CASSCF method with a minimal basis set 6-31G**. Some new equilibrium geometries and transition states have been identified at the CASSCF level. Energetics are also obtained at the QCISD(T)//CASSCF method. Possible reaction paths have been discussed, which are new in literature. Heat of reaction is found to be consistent with the experimental data. Bond dissociation energies to various dissociation paths are also reported.

scholarly journals DFT calculation of the Renner Teller Effect in NCO: Preliminary assessment of Exact Exchange Energy on the accuracy of the X2Π Renner Coefficient

2021 ◽  
Author(s):  
David Kashinski ◽  
Tyler Radziewicz ◽  
Matthew Suarez ◽  
Constantine Stephens ◽  
Edward Byrd
Keyword(s):  
Teller Effect ◽  
Basis Set ◽  
Basis Sets ◽  
Preliminary Assessment ◽  
Molecular Physics ◽  
Dft Methods ◽  
Exact Exchange ◽  
Correlation Consistent ◽  
Bending Modes ◽  
Split Valence

Assessment of DFT methods through analysis of the Renner-Teller Effect (RTE) in the XΠ state of the NCO radical was completed. Our results suggest that the amount of exact exchange at long range is important for an accurate description of the RTE in NCO. DFT functionals from the B3LYP, PBE, TPSS, M06, and M11 families with standard Correlation Consistent, 6-311G split valence family, as well as Sadlej, and Sapporo polarized triple-ζ basis sets were assessed. Our Renner coefficients are compared with previously published theoretical and experimental results to characterize the overall accuracy of various functional/basis set combinations in determining the RTE splitting in the Π (bending) modes of NCO(XΠ). We suggest that this method of analysis can be extended to other systems, serve as an accuracy metric when selecting a functional, and provide a means to create training sets for machine learning in computational molecular physics applications.

BO3 Molecular Structures: Examples of the Importance of Electron Correlation

2008 ◽  
Vol 73 (11) ◽  
pp. 1495-1508 ◽  
Author(s):  
Alexander Yu. Sokolov ◽  
Nathan J. Stibrich ◽  
Henry F. Schaefer
Keyword(s):  
Electron Correlation ◽  
Global Minimum ◽  
Isosceles Triangle ◽  
Molecular Structures ◽  
Basis Set ◽  
Oxygen Species ◽  
Higher Symmetry ◽  
Wide Range ◽  
Spectroscopic Identification ◽  
Correlation Consistent

In 1991 Burkholder and Andrews reported the spectroscopic identification of the boron- oxygen species BO, BO2, B2O2, B2O3, and BO2-. In addition, they tentatively identified two infrared features due to BO3. In this research, a wide range of possible BO3 structures is considered theoretically. The highest level of theory used involves the CCSD(T) method with an augmented correlation consistent quadruple zeta basis set. A planar structure O-B-O-O is predicted to be the global minimum, lying 4.2 kcal mol-1 below a higher symmetry (C2v) structure incorporating a BO2 isosceles triangle. Reasonable agreement is found between the theoretical vibrational frequencies and the two fundamentals reported by Burkholder and Andrews. The potentially important ozone adduct B-O3 is predicted to lie much higher in energy.

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