Quantum chemical B3LYP/cc-pvqz computation of ground-state structures and properties of small molecules with atoms of Z ≤ 18 (hydrogen to argon)(IUPAC Technical Report)

2001 ◽  
Vol 73 (9) ◽  
pp. 1521-1553 ◽  
Author(s):  
Rudolf Janoschek
Keyword(s):  
Small Molecules ◽  
Ground State ◽  
Quantum Chemical ◽  
Density Functional ◽  
Spectroscopic Properties ◽  
Computational Method ◽  
Coupling Constants ◽  
Basis Sets ◽  
General Question ◽  
Absolute Deviation

Since density functional theory (DFT) achieved a remarkable break-through in computational chemistry, the important general question "How reliable are quantum chemical calculations for spectroscopic properties?" should be answered anew. In this project, the most successful density functionals, namely the Becke B3LYP functionals, and the correlation-consistent polarized valence quadruple zeta basis sets (cc-pvqz) are applied to small molecules. In particular, the complete set of experimentally known diatomic molecules formed by the atoms H to Ar (these are 214 species) is uniformly calculated, and calculated spectroscopic properties are compared with experimental ones. Computationally demanding molecules, such as open-shell systems, anions, or noble gas compounds, are included in this study. Investigated spectroscopic properties are spectroscopic ground state, equilibrium internuclear distance, harmonic vibrational wavenumber, anharmonicity, vibrational absolute absorption intensity, electric dipole moment, ionization potential, and dissociation energy. The same computational method has also been applied to the ground-state geometries of 56 polyatomic molecules up to the size of benzene. Special sections are dedicated to nuclear magnetic resonance (NMR) chemical shifts and isotropic hyperfine coupling constants. Each set of systems for a chosen property is statistically analyzed, and the above important question "How reliable...?" is mathematically answered by the mean absolute deviation between calculated and experimental data, as well as by the worst agreement. In addition to presentation of numerous quantum chemically calculated spectroscopic properties, a corresponding updated list of references for experimentally determined properties is presented.

scholarly journals QUANTUM CHEMICAL STUDIES ON BINDING OF cis-[PtCl2(iPram)(Hpz)] TO GUANOSINE

2018 ◽  
Vol 55 (6A) ◽  
pp. 51
Author(s):  
Pham Vu Nhat
Keyword(s):  
Quantum Chemical ◽  
Density Functional ◽  
Spectroscopic Properties ◽  
Basis Sets ◽  
Purine Base ◽  
Base Site ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Correlation Consistent ◽  
Consistent Basis

Quantum chemical calculations are employed to examine the interactions of hydrolysis products of cis-[PtCl2(iPram)(Hpz)] with the purine base site of DNA using guanosine as a model reactant. Thermodynamic parameters, electronic structures, bonding characteristics and spectroscopic properties of the resulting complexes are investigated in the framework of density functional theory (B3LYP functional) along with correlation consistent basis sets. Computed results show that these interactions are dominated by electrostatic effects, namely H-bond contributions. Another remarkable finding is that the replacement of amine groups by larger ones accompanies with a moderate reaction between PtII and guanosine.

Theoretical Study on the Mechanism of Reaction of Ground-State Fe Atoms with Carbon Dioxide

2004 ◽  
Vol 69 (1) ◽  
pp. 13-33 ◽  
Author(s):  
Dimitrios A. Pantazis ◽  
Athanassios C. Tsipis ◽  
Constantinos A. Tsipis
Keyword(s):  
Ground State ◽  
Density Functional ◽  
Activation Barrier ◽  
Spectroscopic Properties ◽  
Basis Sets ◽  
Stationary Points ◽  
Insertion Reaction ◽  
Weakly Bound ◽  
Satisfactory Description ◽  
Bonding Properties

Density functional calculations at the B3LYP level of theory, using the 6-31G(d) and 6-311+G(3df) basis sets, provide a satisfactory description of the geometric and energetic reaction profile of the Fe + CO2 → FeO + CO reaction. The reaction is predicted to be endothermic by 23.24 kcal/mol at the B3LYP/6-311+G(3df)//B3LYP/6-31G(d) level of theory and to proceed by formation of either a Fe(η2-OCO) or a Fe(η3-OCO) intermediate. The Fe(η2-OCO) intermediate in the 5A' ground state is weakly bound with respect to Fe(5D) and CO2 dissociation products by 0.78 (2.88) kcal/mol at the B3LYP/6-31G(d) (B3LYP/6-311+ G(3df)//B3LYP/6-31G(d)) levels of theory. In contrast, the Fe(η3-OCO) intermediate in the 5A1 ground state is unbound with respect to Fe(5D) and CO2 dissociation products by 8.27 (11.15) kcal/mol at the same levels of theory. However, both intermediates are strongly bound relative to the separated Fe+(6D) and [CO2]- anion; the computed bond dissociation energies for the Fe(η2-OCO) and Fe(η3-OCO) intermediates are 207.33 and 198.28 kcal/mol in terms of ∆E0 at the B3LYP/6-31G(d), respectively. In the Fe(η2-OCO) and Fe(η3-OCO) intermediates, an intramolecular insertion reaction of the Fe atom to O-C bond takes place yielding the isomeric OFe(η1-CO) and OFe(η1-OC) products, respectively, with a relatively low activation barrier of 25.24 (21.69) and 26.36 (23.38) kcal/mol at the B3LYP/6-31G(d) (B3LYP/6-311+G(3df)//B3LYP/6-31G(d)) levels of theory, respectively. The calculated structures, relative stability and bonding properties of all stationary points are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution and harmonic vibrational frequencies.

MP2 or B3LYP: computed bond distances compared with CCSD(T)/cc-pVQZ

2018 ◽  
Vol 96 (3) ◽  
pp. 336-339 ◽  
Author(s):  
Delano P. Chong
Keyword(s):  
Small Molecules ◽  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Mean Absolute Deviation ◽  
Slater Type Orbital ◽  
Absolute Deviation ◽  
Bond Lengths ◽  
Hartree Fock ◽  
The Mean

The equilibrium bond lengths of 41 small molecules are calculated by Gaussian09 and ADF2013 programs. We use five different basis sets: 6-31G*, cc-pVDZ, 6-311G+(2d,p), cc-pVTZ, and cc-pVQZ, for six different methods: Hartree-Fock, MP2, MP3, CCSD, CCSD(T), and B3LYP. The reliability of each level of theory on 89 bond lengths compared with CCSD(T)/cc-pVQZ is examined in terms of the mean absolute deviation. In particular, basis set dependence of the relative reliability of the two popular methods MP2 versus B3LYP is important to computational chemists. In addition, the efficient even-tempered basis set of Slater-type orbital called et-pVQZ, available in the ADF2013 program, is tested with the popular density functional B3LYP.

Quantum-Chemical Ab Initio Calculations on Inda- and Thallabenzene (C5H5In and C5H5Tl) and their Structural Isomers η5-C5H5In and η5-C5H5Tl

2018 ◽  
Vol 71 (3) ◽  
pp. 102
Author(s):  
Emma Persoon ◽  
Yuekui Wang ◽  
Gerhard Raabe
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Density Functional ◽  
Single Point ◽  
Normal Modes ◽  
Dft Method ◽  
Basis Sets ◽  
Triplet States ◽  
Structural Isomers ◽  
Td Dft

Quantum-chemical ab initio, time-independent, as well as time-dependent density functional theory (TD-DFT) calculations were performed on the so far elusive heterocycles inda- and thallabenzene (C5H5In and C5H5Tl), employing several different methods (MP2, CISD, CCSD, CCSD(T), BD, BD(T), QCISD, QCISD(T), CASSCF, DFT/B3LYP), effective core potentials, and different basis sets. While calculations on the MP2 level predict the ground states of the title compounds to be singlets with the first triplet states between 13 and 15 kcal mol−1 higher in energy, single point calculations with the QCISD(T), CCSD(T), and BD(T) methods at CCSD-optimized structures result in energy differences between the singlet and the triplet states in the range between 0.3 and 2.1 kcal mol−1 in favour of the triplet states. According to a CASSCF(8,8) calculation the triplets are also more stable by about 2.5–2.9 kcal mol−1. Calculations were also performed for the C5v-symmetric η5 structural isomers (cyclopentadienylindium, CpIn, and cyclopentadienylthallium, CpTl, Cp = C5H5) of the title compounds. At the highest level of theory employed in this study, C5H5In is between 79 and 88 kcal mol−1 higher in energy than CpIn, while this energy difference is even larger for thallabenzene where C5H5Tl is energetically between 94 and 102 kcal mol−1 above CpTl. In addition we report on the UV/vis spectra calculated with a TD-DFT method as well as on the spectra of the normal modes of C5H5In and C5H5Tl. Both types of spectra might facilitate identification of the title compounds eventually formed in photolysis or pyrolysis experiments.

Quantum-Chemical Ab Initio Calculations on Ala-(C5H5Al) and Galabenzene (C5H5Ga)

2014 ◽  
Vol 69 (7) ◽  
pp. 349-359 ◽  
Author(s):  
Stefanie Mersmann ◽  
Halima Mouhib ◽  
Matthias Baldofski ◽  
Gerhard Raabe
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Density Functional ◽  
Normal Modes ◽  
Closed Shell ◽  
Basis Sets ◽  
Moderate Intensity ◽  
Spectral Curves ◽  
Singlet States ◽  
Td Dft

1Quantum-chemical ab initio and time-dependent density functional theory (TD-DFT) calculations employing various basis sets were used to elucidate the spatial as well as the electronic structure of C5H5Al () and C5H5Ga (2) (ala- and galabenzene). The lowest closed shell singlet states of both compounds were found to have a non-planar structure of CS symmetry with C-X-C bond angles of about 116° (MP2/6-311++G**) and 125° (CCSD/aug-cc-pVDZ). At approximately 103°, the corresponding angles of the lowest triplets are significantly smaller. The lowest triplet state of alabenzene is also non-planar (CS) at the MP2 level while optimization with the CCSD and the CASPT2 method resulted in planar structures with C2v symmetry. The corresponding state of galabenzene has C2v symmetry at all levels of optimization. The relative stability of the lowest closed shell singlet and the lowest triplet (ΔE(T1-S0)) state is small and its sign even strongly method-dependent. However, according to the highest levels of theory applied in this study the singlet states of both molecules are slightly lower in energy than the corresponding triplets with singlet/triplet gaps between about 0.5 and 5.8 kcal/mol in favour of the singlet states. Most of the applied methods give a slightly smaller splitting for ala- than for galabenzene. Independent of the applied method (TD-DFT/CAM-B3LYP/6-311++G(3df,3pd)//MP2/6- 311++G** or SAC-CI/6-31++G(3df,3pd)//MP2/6-311++G**), the general shape of the calculated UV/VIS spectral curves are quite similar for the lowest singlet states of ala- and galabenzene, and the same applies to the spectra of the normal modes. The calculated UV/VIS spectra of C5H5Al and C5H5Ga are featured by long wavelength bands of moderate intensity around 900 nm at the TD-DFT and between 1300 and 1500 nm at the SAC-CI level. According to both methods these bands are predominantly due to HOMO(π)→LUMO(σ*) transitions. The results of isodesmic bond separation reactions for the singlet states indicate some degree of stabilization due to delocalization in both of the title compounds. With our best values between 29 and 32 kcal/mol this stabilization appears to be only slightly less than the previously reported value for borabenzene (∼38 kcal/mol).

Density Functional Study of the Electronic Structure and Related Properties of Pt(NO)/Pt(NO2) Redox Couples

2003 ◽  
Vol 68 (3) ◽  
pp. 423-446 ◽  
Author(s):  
Paraskevas Karipidis ◽  
Athanassios C. Tsipis ◽  
Constantinos A. Tsipis
Keyword(s):  
Ground State ◽  
Density Functional ◽  
Activation Barrier ◽  
Spectroscopic Properties ◽  
Redox Couple ◽  
Basis Set ◽  
Stationary Points ◽  
Functional Study ◽  
Dft Theory ◽  
Exothermic Process

Density functional calculations at the B3LYP level of theory, using the SDD basis set, provide satisfactory description of geometric, energetic, electronic and spectroscopic properties of the Pt(NO)/Pt(NO2) redox couple. The neutral Pt(NO) species adopts a bent 2A' ground state, while the cationic [Pt(NO)]+ species adopts a linear 1Σ+ ground state. The B3LYP/SDD- predicted Pt-N bond lengths are 2.016 and 1.777 Å for Pt(NO) (2A') and [Pt(NO)]+ (1Σ+), respectively, while the ∠Pt-N-O bent angle for [Pt(NO)] (2A') is 119.6°. On the other hand, the anionic [Pt(NO)]- species adopts the bent 1A' ground state with a Pt-N bond length of 1.867 Å and a ∠Pt-N-O bent angle of 122.5°. The computed binding energies of the NO, NO+ and NO- ligands with Pt(0) were found to be 29.9 (32.8), 69.9 (78.4) and 127.4 (128.7) kcal/mol at the B3LYP/SDD and CCSD(T)/SDD (numbers in parentheses) levels of theory, respectively. Moreover, the structure of the [Pt(NO2)]+ component of the Pt(NO)/Pt(NO2) redox couple and its transformation to [Pt(NO)]+ upon reaction with CO was analysed in the framework of the DFT theory. The coordination of the CO ligand to [Pt(NO2)]+ affords the cationic mixed-ligand [Pt(CO)(NO2)]+ complex, which is stabilized by 66.6 (60.5) kcal/mol, with respect to the separated [Pt(NO2)]+ and CO in their ground states. The O-transfer reaction from the coordinated NO2 to the coordinated CO ligands in the presence of the [Pt(NO2)]+ species corresponds to an exothermic process; the heat of the reaction (∆RH) is -85.2 (-80.5) kcal/mol and the activation barrier amounts to 27.7 (33.0) kcal/mol. Finally, the equilibrium structures of selected stationary points related to the transformation of NO to NO2 ligand located on the potential energy surfaces of the [Pt(NO),O2], [Pt(NO)+,O2], and [Pt(NO)-,O2] systems were analysed in the framework of the DFT theory. The computed interaction energies of O2 with Pt(NO), [Pt(NO)]+ and [Pt(NO)]- species were found to be 106.9 (105.3), 49.2 (48.4) and 26.9 (26.5) kcal/mol, respectively. The O2 ligand is coordinated to the Pt central atom in an end-on mode for [Pt(NO),O2] and [Pt(NO)-,O2] systems and in a side-on mode for the [Pt(NO)+,O2] system. The transformation of NO to NO2 in [Pt(NO)]- species upon reaction with dioxygen corresponds to an exothermic process; the heat of the reaction (∆RH) is -60.6 (-55.8) kcal/mol, while the activation barrier amounts to 35.5 (30.2) kcal/mol. Calculated structures, relative stability and bonding properties of all stationary points are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution and harmonic vibrational frequencies.

scholarly journals Hyperfine Coupling Constants in Local Exact Two-Component Theory

2021 ◽  
Author(s):  
Yannick J. Franzke ◽  
Jason M. Yu
Keyword(s):  
Single Molecule ◽  
Density Functional ◽  
Hyperfine Coupling ◽  
Scalar Potential ◽  
Coupling Constants ◽  
Basis Set ◽  
Basis Sets ◽  
Spin Orbit ◽  
Finite Nucleus ◽  
Two Component

We present a highly efficient implementation of the electron-nucleus hyperfine coupling matrix within one-electron exact two-component (X2C) theory. The complete derivative of the X2C Hamiltonian is formed, i.e. the derivatives of the unitary decoupling transformation are considered. This requires solution of the response and Sylvester equations, consequently increasing the computational costs. Therefore, we apply the diagonal local approximation to the unitary decoupling transformation (DLU). The finite nucleus model is employed for both the scalar potential and the vector potential. Two-electron picture-change effects are modeled with the (modified) screened-nuclear spin--orbit approach. Our implementation is fully integral direct and OpenMP-parallelized. An extensive benchmark study regarding the Hamiltonian, the basis set, and the density functional approximation is carried out for a set of 12--17 transition-metal compounds. The error introduced by DLU is negligible and the DLU-X2C Hamiltonian accurately reproduces its four-component ``fully'' relativistic parent results. Functionals with a large amount of Hartree--Fock exchange such as CAM-QTP-02 and omega-B97X-D are generally favorable. The pure density functional r2SCAN performs remarkably and even outperforms the common hybrid functionals TPSSh and CAM-B3LYP. Fully uncontracted basis sets or contracted quadruple-zeta bases are required for accurate results. The capability of our implementation is demonstrated for [Pt(C6Cl5)4]- with more than 4700 primitive basis functions and four rare-earth single molecule magnets: [La(OAr*)3]-, [Lu(NR2)3]-, [Lu(OAr*)3]-, and [TbPc2]-. Here, the spin--orbit DLU-X2C Hamiltonian results in an excellent agreement with the experimental findings of all Pt, La, Lu, and Tb molecules.

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