CHARACTERIZATION OF THE $\tilde{X}\,^2 \Pi$ AND Ã2Σ+ ELECTRONIC STATES OF THE PHOSPHAETHYNE CATION (HCP+)

2005 ◽  
Vol 04 (spec01) ◽  
pp. 707-724 ◽  
Author(s):  
BERHANE TEMELSO ◽  
NANCY A. RICHARDSON ◽  
LEVENT SARI ◽  
YUKIO YAMAGUCHI ◽  
HENRY F. SCHAEFER
Keyword(s):  
Ground State ◽  
Dipole Moments ◽  
Basis Set ◽  
Basis Sets ◽  
Structure Theory ◽  
Coupled Cluster ◽  
Excitation Energies ◽  
State Formula ◽  
Correlation Consistent ◽  
Experimental Values

The electronic ground state [Formula: see text] and first excited state (Ã2Σ+) of phosphaethyne cation (HCP+) have been systematically investigated using ab initio electronic structure theory. The total energies, geometries, rotational constants, dipole moments, harmonic vibrational frequencies, and parameters for Renner–Teller splittings were determined using self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster (CC) with single and double excitations (CCSD), CCSD with perturbative triple excitations [CCSD(T)], CC with single, double, and iterative partial triple excitations (CCSDT-3), and CC with single, double, and full triple excitations (CCSDT) methods and eight different basis sets. Some of the largest full triples coupled cluster computations to date are reported. Degenerate bending frequencies for the Ã2Σ+ state were determined using the equation-of-motion (EOM)-CCSD technique. The two states have been confirmed to have linear equilibrium structures. At the full CCSDT level of theory with the correlation-consistent polarized valence quadruple zeta (cc-pVQZ) basis set, the classical [Formula: see text] splitting ( T e value) is predicted to be 47.7 kcal/mol (2.07 eV, 16,700 cm-1) and the quantum mechanical splitting (T0 value) to be 48.1 kcal/mol (2.08 eV, 16,800 cm-1), which are in excellent agreement with the experimental values of T e = 47.77 kcal/mol (2.072 eV , 16,708 cm -1) and T0 = 47.94 kcal/mol (2.079 eV, 16,766 cm-1). The excitation energies predicted by the CCSDT-3 and CCSD(T) methods differ from the full triples CCSDT result by 0.38 and 0.45 kcal/mol, respectively. With the aug-cc-pVQZ CCSDT-3 method the Renner parameter and the averaged harmonic bending vibrational frequency are determined to be ∊= -0.0390 and [Formula: see text] for the ground state of HCP+, which are reasonably consistent with the experimental values of ∊=-0.0415 and [Formula: see text]. The predicted dipole moments are 1.30 Debye ([Formula: see text] state, polarity-hydrogen atom positive) and 0.06 Debye (Ã2Σ+ state, polarity-phosphorus atom positive).

Accuracy Assessment of the ROHF-CCSD(T) Calculationsof Dipole Moments of Small Radicals

1998 ◽  
Vol 63 (9) ◽  
pp. 1409-1430 ◽  
Author(s):  
Miroslav Urban ◽  
Pavel Neogrády ◽  
Juraj Raab ◽  
Geerd H. F. Diercksen
Keyword(s):  
Large Deviation ◽  
Theoretical Calculations ◽  
Dipole Moments ◽  
Accuracy Assessment ◽  
Open Shell ◽  
Basis Set ◽  
Coupled Cluster ◽  
Hartree Fock ◽  
Experimental Values

Dipole moments of a series of radicals, OH, NO, NS, SF, SO, PO, ClO, CN, LiO, NO2, and ClO2 were calculated by the Coupled Cluster CCSD(T) method with the single determinant restricted open shell Hartree-Fock (ROHF) reference. For all molecules theoretical dipole moments were carefully compared to experimental values. The size and the quality of the basis set were systematically improved. Spin adaptation in the ROHF-CCSD(T) method, largest single and double excitation amplitudes and the T1 diagnostics were considered as indicators in the quality assessment of calculated dipole moments. For most molecules the accuracy within 0.01-0.03 D was readily obtained. For ClO and CN the spin adaptation was necessary - its contribution was as large as 0.03-0.045 D. Large deviation from experiment is observed for OH in its A2Σ+ excited state (0.135 D) and especially for LiO in its 2Π ground state (0.22 D). No indication of the failure of theoretical calculations was found which leads to the conclusion that, even if there is still a space for the improvement of theoretical calculations, experimental values should be reconsidered.

Electron Affinities of BN, NO and NF: Coupled Cluster and Multireference Configuration Interaction Calculations

2005 ◽  
Vol 70 (7) ◽  
pp. 923-940 ◽  
Author(s):  
Jiří Fišer ◽  
Rudolf Polák
Keyword(s):  
Configuration Interaction ◽  
Relativistic Effects ◽  
Basis Set ◽  
Basis Sets ◽  
Spectroscopic Constants ◽  
Coupled Cluster ◽  
Electron Affinities ◽  
Complete Basis Set ◽  
Correlation Consistent ◽  
Consistent Basis

The accurate adiabatic electron affinities (EA) of the BN, NO and NF molecules have been determined using the coupled cluster approach and multireference configuration interaction methods. By combining large doubly augmented correlation-consistent basis sets (through the sextuple zeta) and complete basis set extrapolations with corrections for core-valence correlation and relativistic effects, we find that the RCCSD(T) method gives EA(BN) = 3.153 eV in very close agreement with experiment and predicts EA(NF) = 0.247 eV. The RCCSD(T) and UCCSD(T) EA(NO) results, 0.008 and 0.031 eV, bracket the experimental value. For both the neutral and anionic ground state species the usual spectroscopic constants were derived.

Theoretical studies on the absorption and luminescent properties of a series of derivatives of 1,3-diphenyl-5-pyrene-2-yl-4,5-dihydro-1H-pyrazole

2005 ◽  
Vol 83 (2) ◽  
pp. 166-173 ◽  
Author(s):  
Xiao-Juan Liu ◽  
Ji-Kang Feng ◽  
Ai-Min Ren ◽  
Xin Zhou ◽  
Hong Cheng
Keyword(s):  
Ground State ◽  
Emission Spectra ◽  
Luminescent Properties ◽  
Basis Set ◽  
Basis Sets ◽  
Absorption And Emission ◽  
Reaction Field ◽  
Hartree Fock ◽  
Polarized Continuum Model ◽  
Experimental Values

The absorption and emission spectra for a series of substituted 1,3-diphenyl-5-pyrene-2-yl-4,5-dihydro-1H-pyrazole (DPPyP) molecules are computed by TDDFT methods. The solvent effect is modeled using the self-consistent reaction field (SCRF) method with Tomasi's polarized continuum model (PCM). The ground-state geometries were optimized by the Hartree–Fock method with the 6-31G basis set (and also with 3-21G* for molecule A) (HF/6-31G), and the lowest singlet excited-state geometries were optimized at the ab initio CIS level with the 6-31G basis set (CIS/6-31G). The calculated results indicate that the TDDFT method can reproduce the experimental values. We consider the effects of different basis sets on the optimization of the ground-state geometries. Specially, some insights on the differences observed for these compounds in changing the substituted donors (H, CH3, and NH2) and acceptor group (CN) are given; the results indicate that introduction of the donor groups will lead emission to be red-shifted, while introduction of the acceptor will induce the emission to be blue-shifted, which provides useful information for modulating light-emitting material colors.Key words: absorption and emission, TDDFT, CIS, SCRF–PCM.

scholarly journals Eine SCF-MO-CI-Berechnung des C2 -Moleküls mit einer atomaren Basis von kontrahierten Gauß-Funktionen / An scf-mo-cl calculation of the c2 molecule using an atomic basis of contracted gaussian lobe functions

1972 ◽  
Vol 27 (7) ◽  
pp. 1031-1041 ◽  
Author(s):  
J Barsuhn
Keyword(s):  
Experimental Data ◽  
Basis Set ◽  
Basis Sets ◽  
Excitation Energies ◽  
Experimental Values ◽  
Extensive Experimental Data ◽  
The Relationship ◽  
Ci Calculations ◽  
State Configuration ◽  
Slater Basis

Abstract The C2-molecule seems to be a very useful object for the purpose of comparing different quantum chemical calculations because of the extensive experimental data available for this molecule. In the present treatment a basis set consisting of 25 primitive Gaussian lobe functions which have been contracted into 4 s-groups and 2X3 p-groups has been used. SCF orbitals obtained for the ground state configuration 1 πu4 have been employed in two CI-calculations at R-values in the vicinity of the equilibrium internuclear distance. The calculation involving only virtual a-orbitals agrees qualitatively with the experimental data for the three known Rydberg states. The most extensive Cl-treatment employed overestimates the excitation energies to the higher states by up to 1.7 eV; the relationship between the theoretically calculated transition energies and the corresponding experimental values is approximately linear, however. The results are compared with previous extensive CI-calculations of FOUGERE and NESBET who used two different 2-zeta Slater basis sets

Electronic Structure and Bonding Nature of the Ground State Monocarbide Cations, ScC+, TiC+, VC+, and CrC+

2003 ◽  
Vol 68 (2) ◽  
pp. 387-404 ◽  
Author(s):  
Ioannis S. K. Kerkines ◽  
Aristides Mavridis
Keyword(s):  
Ground State ◽  
Ground States ◽  
Relativistic Effects ◽  
Zero Point ◽  
Basis Set ◽  
Basis Sets ◽  
Energy Separation ◽  
Full Potential ◽  
Complete Basis Set ◽  
Correlation Consistent

The ground states of the transition-metal diatomic carbide cations, MC+ (M = Sc, Ti, V, and Cr), are studied using multireference configuration interaction (MRCI) methods in conjunction with quantitative basis sets. Full potential energy curves are calculated for all four systems. When 3s23p6 core/valence correlation contributions and scalar relativistic effects are taken into account, our best estimates for the zero-point-corrected dissociation energies of the MC+ series are in good agreement with relevant experimental results. For TiC+, the recent correlation-consistent-type basis sets for Ti of Bauschlicher are also exploited to extract complete basis set limits of selected properties. The ground states of VC+(X 3∆) and CrC+(X 2∆) are reported for the first time in the literature. For CrC+ an interesting competition is revealed between the 2∆ and 4Σ- states; although 4Σ- is formally the ground state at the MRCI level of theory, when core/valence and/or relativistic effects are included, the ground state of CrC+ becomes of 2∆ symmetry, with a calculated energy separation (a 4Σ- ← X 2∆) of 2.3 kcal/mol.

THE EXOTHERMIC PNC → PCN REACTION

2006 ◽  
Vol 05 (02) ◽  
pp. 281-297 ◽  
Author(s):  
SUYUN WANG ◽  
YUKIO YAMAGUCHI ◽  
HENRY F. SCHAEFER
Keyword(s):  
Transition State ◽  
Dipole Moments ◽  
Bond Distance ◽  
Zero Point ◽  
Open Shell ◽  
Basis Sets ◽  
Structure Theory ◽  
Isomerization Reaction ◽  
Linear Formula ◽  
Correlation Consistent

PCN and PNC are possible interstellar species that have not been experimentally characterized. With various ab initio methods, including multireference and restricted open-shell single-reference electronic structure theory, the PCN/PNC species and the transition state for the isomerization reaction PCN ↔ PNC have been studied. The Dunning series of correlation-consistent basis sets, cc-pVXZ and aug-cc-pVXZ (X = T and Q), have been used. Geometries, total energies, dipole moments, harmonic vibrational frequencies, infrared intensities, and zero-point vibrational energies are reported for the PCN/PNC isomers and the transition state. Both PCN and PNC are linear with 3Σ- ground states, and linear [Formula: see text] is predicted to lie 13.7 kcal mol-1 (13.5 kcal mol-1 with ZPVE correction) above linear [Formula: see text] at the aug-cc-pVQZ CCSD(T) level of theory. The CN bond distance in [Formula: see text] is predicted to be 1.174 Å, only 0.002 Å longer than the experimental value of 1.172 Å for diatomic CN (X2Σ+, suggesting that CN has triple bond character in [Formula: see text]. The isomerization transition state is found to be cyclic [Formula: see text], with angles θ e ( PCN ) = 82.2°, θ e ( CNP ) = 63.1°, and θ e ( NPC ) = 34.7°. The isomerization barrier is predicted to be 35.7 kcal mol-1 (34.5 kcal mol-1 with ZPVE correction) relative to linear [Formula: see text]. The predicted dipole moments are substantial, 2.79 debye (polarity + PCN -) and 2.51 debye (polarity + PNC -).

Ab initio electronic structure and direct dynamics simulations of CH3OCl

2009 ◽  
Vol 87 (7) ◽  
pp. 1022-1029
Author(s):  
Stephanie Y. Y. Wong ◽  
Pierre-Nicholas Roy ◽  
Alex Brown
Keyword(s):  
Electronic Structure ◽  
Excited State ◽  
Ab Initio ◽  
Ground State ◽  
Basis Set ◽  
Ab Initio Molecular Dynamics ◽  
Basis Sets ◽  
Excitation Energies ◽  
Direct Dynamics ◽  
Ab Initio Electronic Structure

The ground (X1A′) and two lowest lying excited singlet states (11A″ and 21A′) of methyl hypochlorite have been examined using ab initio electronic structure techniques to validate computationally efficient methods, upon which direct dynamics can be based, versus high-level ones, for which direct dynamics would be intractable. Ground-state equilibrium geometries and vibrational frequencies determined using density functional theory (DFT) with the 6-31G(d) basis set are tested against coupled-cluster theory (CCSD(T)) results from the literature. Vertical excitation energies and transition dipole moments calculated at the complete active space self-consistent field CASSCF/6-31+G(d) level of theory are benchmarked against multireference configuration interaction (MRCI) results with the aug-cc-pVXZ (X = D, T, Q) family of basis sets. The excited-state gradients that will govern the classical dynamics are compared for CASSCF/6-31+G(d) versus MRCI/aug-cc-pVXZ (X = D, T). To carry out the ab initio molecular dynamics (AIMD), existing electronic structure codes have been interfaced with the molecular modelling toolkit (MMTK), an open-source program library for molecular simulation applications. We use two examples to demonstrate the use of direct dynamics in MMTK: a canonical ground-state trajectory to sample positions and momenta, and an excited-state microcanonical trajectory based on CASSCF. The work presented here forms the basis for future study of the photodissociation of CH3OCl. As well, the implementation of AIMD within MMTK provides a useful tool for examining a variety of other research problems.

Group IIIa Hydrides XH2 and XH2- (X = B, Al, Ga): Electron Affinities and Singlet-Triplet Splittings Revisited

2003 ◽  
Vol 68 (1) ◽  
pp. 75-88 ◽  
Author(s):  
Ivan Černušák ◽  
Alena Zavažanová ◽  
Juraj Raab ◽  
Pavel Neogrády
Keyword(s):  
Ground State ◽  
Basis Set ◽  
Basis Sets ◽  
Coupled Cluster ◽  
Electron Affinities ◽  
Complete Basis ◽  
Complete Basis Set ◽  
Order Of Magnitude ◽  
Complete Basis Set Limit ◽  
Cluster Methods

Geometries, electron affinities (EA) and singlet-triplet (S-T) splittings of XH2/XH2- molecules (X = B, Al, Ga) are calculated by coupled-cluster methods, using the sequence of basis sets. The EA values and S-T splittings for aluminium and gallium dihydrides are an order of magnitude larger (in absolute values) than those for boron. For boron and aluminium dihydrides, two types of extrapolations towards complete basis set limit are applied, leading to EA = 0.24 eV, ST = -0.01 eV (BH2), and EA = 1.10 eV, ST = -0.62 eV. The best calculated values for gallium dihydrides are EA = 1.13 eV and ST = -0.74 eV. All three S-T splittings favour singlet as the ground state, although the S-T splittings of BH2- is exceptionally small. In addition, vertical electron affinities and vertical electron detachments are reported for these molecules.

DFT Benchmark Study of the O--O Bond Dissociation Energy in Peroxides Validated with High-Level Ab-Initio Calculations

2019 ◽  
Author(s):  
Danilo Carmona ◽  
Pablo Jaque ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Reference Value ◽  
Basis Set ◽  
Basis Sets ◽  
Mean Deviation ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
The Mean ◽  
Experimental Values ◽  
High Level ◽  
Almost All

<div><div><div><p>Peroxides play a central role in many chemical and biological pro- cesses such as the Fenton reaction. The relevance of these compounds lies in the low stability of the O–O bond which upon dissociation results in radical species able to initiate various chemical or biological processes. In this work, a set of 64 DFT functional-basis set combinations has been validated in terms of their capability to describe bond dissociation energies (BDE) for the O–O bond in a database of 14 ROOH peroxides for which experimental values ofBDE are available. Moreover, the electronic contributions to the BDE were obtained for four of the peroxides and the anion H2O2− at the CBS limit at CCSD(T) level with Dunning’s basis sets up to triple–ζ quality provid- ing a reference value for the hydrogen peroxide anion as a model. Almost all the functionals considered here yielded mean absolute deviations around 5.0 kcal mol−1. The smallest values were observed for the ωB97 family and the Minnesota M11 functional with a marked basis set dependence. Despite the mean deviation, order relations among BDE experimental values of peroxides were also considered. The ωB97 family was able to reproduce the relations correctly whereas other functionals presented a marked dependence on the chemical nature of the R group. Interestingly, M11 functional did not show a very good agreement with the established order despite its good performance in the mean error. The obtained results support the use of similar validation strategies for proper prediction of BDE or other molecular properties by DF Tmethods in subsequent related studies.</p></div></div></div>

Application of multireference linearized coupled-cluster theory to atomic and molecular systems

2018 ◽  
Vol 17 (02) ◽  
pp. 1850016 ◽  
Author(s):  
Jiang Yi ◽  
Feiwu Chen
Keyword(s):  
Ground State ◽  
Basis Sets ◽  
Coupled Cluster ◽  
Vibration Frequencies ◽  
Electron Affinities ◽  
Proton Affinities ◽  
Coupled Cluster Theory ◽  
Molecular Systems ◽  
Ground State Energies ◽  
Second Order Perturbation Theory

Applications of the multireference linearized coupled-cluster single-doubles (MRLCCSD) to atomic and molecular systems have been carried out. MRLCCSD is exploited to calculate the ground-state energies of HF, H2O, NH3, CH4, N2, BF, and C2with basis sets, cc-pVDZ, cc-pVTZ and cc-pVQZ. The equilibrium bond lengths and vibration frequencies of HF, HCl, Li2, LiH, LiF, LiBr, BH, and AlF are computed with MRLCCSD and compared with the experimental data. The electron affinities of F and CH as well as the proton affinities of H2O and NH3are also calculated with MRLCCSD. These results are compared with the results produced with second-order perturbation theory, linearized coupled-cluster doubles (LCCD), coupled-cluster doubles (CCD), coupled-cluster singles and doubles (CCSD), CCSD with perturbative triples correction (CCSD(T)). It is shown that all results obtained with MRLCCSD are reliable and accurate.

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