Ab Initio Studies on Amides: Cyanamide, Dicyanamide and Tricyanamide

1985 ◽  
Vol 38 (6) ◽  
pp. 835 ◽  
Author(s):  
NV Riggs ◽  
L Radom
Keyword(s):  
Nitrogen Atom ◽  
Ab Initio ◽  
Basis Set ◽  
Basis Sets ◽  
Pyramidal Structure ◽  
Bond Lengths ◽  
Planar Form ◽  
Planar Molecules ◽  
Experimental Values ◽  
Experimental Geometry

Optimization of the geometry of cyanamide with the 3-21G basis set leads to a planar (C2v) structure, whereas the STO-3G, 6-31G* and 6- 31G** basis sets lead to a pyramidal structure at the amido -nitrogen atom. The 6-31G* and 6-31G** geometries are reasonably close to the experimental geometry, and the calculated barriers to inversion (4.5 and 3.4 kJ mol-1, respectively) are also close to experimental values (5.4-5.6 kJ mol-1), but the STO-3G value (13.9 kJ mol-1) is much too high. Dicyanamide is far from planar at the STO-3G level but planar at the more definitive 6-31G* level, whereas tricyanamide is planar even at the STO-3G level. The prediction is that, in contrast to cyanamide itself, dicyanamide and tricyanamide are planar molecules. Calculated increases in N-C bond-lengths and decreases in C≡N bond-lengths for dicyanamide and tricyanamide as compared with the planar form of cyanamide are used to predict experimental lengths for these bonds in di - and tri- cyanamide.

The simplified ab initio method calculation of linear polarizability

1973 ◽  
Vol 26 (5) ◽  
pp. 921 ◽  
Author(s):  
RD Brown ◽  
GR Williams
Keyword(s):  
Ab Initio ◽  
Small Molecules ◽  
Basis Set ◽  
Basis Sets ◽  
Orbital Method ◽  
Polarizability Anisotropy ◽  
Minimal Basis ◽  
Hartree Fock ◽  
Numerical Performance ◽  
Experimental Values

The simplified ab-initio molecular-orbital method described previously is particularly suited to the calculation of polarizabilities by the non-perturbative coupled Hartree-Fock technique. Trial calculations on CO and HF, for which comparison with corresponding ab-initio calculations is possible, show that the method gives an adequate numerical performance. Minimal basis set calculations in general tend to give values that are considerably too low because of inadequate flexibility of the basis and this is the origin of the large discrepancy between theory and experiment, especially for small molecules. ��� Results are also reported for N2O and O3. For these larger systems the SAI results with minimal basis sets are noticeably nearer experimental values. The polarizability anisotropy for N2O is particularly well reproduced by the SAI method. �

A Systematic DFT Study of Two Elementary Steps Involving Hydrogen Peroxide and the Hydroxyl Radical in the Fenton Reaction

2018 ◽  
Author(s):  
Danilo Carmona ◽  
David Contreras ◽  
Oscar A. Douglas-Gallardo ◽  
Stefan Vogt-Geisse ◽  
Pablo Jaque ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Hydroxyl Radical ◽  
Ab Initio ◽  
Fenton Reaction ◽  
Basis Set ◽  
Basis Sets ◽  
Dft Methods ◽  
Elementary Steps ◽  
Oxygen Oxygen ◽  
Complete Basis Set

The Fenton reaction plays a central role in many chemical and biological processes and has various applications as e.g. water remediation. The reaction consists of the iron-catalyzed homolytic cleavage of the oxygen-oxygen bond in the hydrogen peroxide molecule and the reduction of the hydroxyl radical. Here, we study these two elementary steps with high-level ab-initio calculations at the complete basis set limit and address the performance of different DFT methods following a specific classification based on the Jacob´s ladder in combination with various Pople's basis sets. Ab-initio calculations at the complete basis set limit are in agreement to experimental reference data and identified a significant contribution of the electron correlation energy to the bond dissociation energy (BDE) of the oxygen-oxygen bond in hydrogen peroxide and the electron affinity (EA) of the hydroxyl radical. The studied DFT methods were able to reproduce the ab-initio reference values, although no functional was particularly better for both reactions. The inclusion of HF exchange in the DFT functionals lead in most cases to larger deviations, which might be related to the poor description of the two reactions by the HF method. Considering the computational cost, DFT methods provide better BDE and EA values than HF and post--HF methods with an almost MP2 or CCSD level of accuracy. However, no systematic general prediction of the error based on the employed functional could be established and no systematic improvement with increasing the size in the Pople's basis set was found, although for BDE values certain systematic basis set dependence was observed. Moreover, the quality of the hydrogen peroxide, hydroxyl radical and hydroxyl anion structures obtained from these functionals was compared to experimental reference data. In general, bond lengths were well reproduced and the error in the angles were between one and two degrees with some systematic trend with the basis sets. From our results we conclude that DFT methods present a computationally less expensive alternative to describe the two elementary steps of the Fenton reaction. However, choice of approximated functionals and basis sets must be carefully done and the provided benchmark allows a systematic validation of the electronic structure method to be employed

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>

scholarly journals Stable Occupancy of Hydrogen Molecules in Clathrate Hydrates and + THF Clathrate Hydrates Determined by Ab Initio Calculations

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
Prasad Yedlapalli ◽  
Sangyong Lee ◽  
Jae W. Lee
Keyword(s):  
Ab Initio ◽  
Binding Energies ◽  
Clathrate Hydrates ◽  
Basis Set ◽  
Large Cavity ◽  
Basis Sets ◽  
Pure Hydrogen ◽  
Point Energy ◽  
Small Cavity ◽  
Hydrogen Molecules

Structure II clathrate hydrates of pure hydrogen and binary hydrates of are studied using ab initio calculations to determine the stable occupancies of small cavities. Ab initio calculations are carried out for a double cavity consisting of one dodecahedron (small cavity) and one hexakaidecahedron (large cavity). These two cavities are attached to each other as in sII hydrates to form a double cavity. One or two molecules are placed in the small cavity and one THF (or 4 molecules) molecule is placed in the large cavity. We have determined the binding energies of the double cavities at the MP2 level using various basis sets (3-21G, 3-21G(2p), 3-21 G(2p), 6-31G, 6-31G(2p), and 6-31 G(2p)). Different basis sets yield different stable occupancies of the small cavity. The results from the highest basis set (6-31 G(2p) with zero point energy corrections) indicate that the single occupancy is slightly more favorable than the double occupancy in both the cases of pure hydrates and THF + double hydrates.

The structure and energetics of low-lying states of RCO and RNN free radicals

1977 ◽  
Vol 55 (5) ◽  
pp. 863-868 ◽  
Author(s):  
N. Colin Baird ◽  
Harish B. Kathpal
Keyword(s):  
Experimental Data ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Open Shell ◽  
Basis Set ◽  
Basis Sets ◽  
Mo Calculations ◽  
Decomposition Products ◽  
Ab Initio Mo Calculations

The important geometrical variables in the structures of the lowest 2A′ and 2A′′ states of the free radicals HCO, CH3CO, NH2CO, HNN, and CH3NN have been determined by ab initio MO calculations using the STO-3G basis set. The energy differences between the states, and the energies of the radicals relative to their decomposition products and relative to their hydrogen atom addition products, are reported using both STO-3G and 4-31G basis sets in the restricted open-shell calculations. The trends in these results and their relation to available experimental data are discussed.

AB-INITIO MOLECULAR DYNAMICS IN THE FULL-POTENTIAL LMTO METHOD: DERIVATION OF A PRACTICAL FORCE THEOREM

1993 ◽  
Vol 07 (01n03) ◽  
pp. 262-265 ◽  
Author(s):  
M. METHFESSEL ◽  
M. VAN SCHILFGAARDE
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Local Density ◽  
Basis Set ◽  
Ab Initio Molecular Dynamics ◽  
Basis Sets ◽  
Full Potential ◽  
Major Advance ◽  
First Results ◽  
Lmto Method

A major advance in electronic structure calculations was the combination of local-density techniques with molecular dynamics by Car and Parrinello seven years ago. Unfortunately, application of the Car-Parrinello scheme has been limited essentially to sp materials because only in the plane-wave pseudopotential method forces are trivial to calculate. We present a systematic approach to derive force theorems with desired characteristics within complicated basis sets, which are applicable to all elements of the periodic table equally well. Application to the LMTO basis set yields an accurate force theorem, quite distinct from the Hellman-Feynman form, which is exceptionally insensitive to errors in the trial density. The forces were implemented in a new full-potential LMTO method which is suited to arbitrary geometries. First results for ab-initio molecular dynamics and simulated annealing runs are shown for some random small molecules and small clusters of silver atoms.

Computational Procedure of Lattice Energy Using the Ab Initio MO Method

2003 ◽  
Vol 02 (02) ◽  
pp. 233-244 ◽  
Author(s):  
Kanade Nagayoshi ◽  
Tohru Ikeda ◽  
Kazuo Kitaura ◽  
Shigeru Nagase
Keyword(s):  
Ab Initio ◽  
Molecular Crystals ◽  
Lattice Energy ◽  
Computational Procedure ◽  
Basis Set ◽  
Full Account ◽  
Packing Structure ◽  
Donor Acceptor ◽  
Ab Initio Mo ◽  
Experimental Values

Recently, we have proposed a computational procedure for calculations of lattice energies of molecular crystals using the ab initio MO method. This procedure does not use potential functions and is applicable to a variety of molecular crystals. The procedure has been successfully applied to calculation of packing structure of electron donor-acceptor complex, H3N–BF3, and hydrogen bonding crystal, CH3OH. In this work, we present a full account of the computational procedure. This method is applied to the packing structure calculations of hydrocarbon crystals, C2H2, C2H4 and C6H6. The lattice parameters optimized at the MP2/6-311++G** level are in good agreement with the experimental values. The basis set dependence of the lattice constants is also discussed for several crystals.

Bond order-bond length relationships in conjugated hydrocarbons - the microwave spectrum and structure of 3,4-dimethylenecyclobutene

1983 ◽  
Vol 36 (4) ◽  
pp. 639 ◽  
Author(s):  
RD Brown ◽  
PD Godfry ◽  
BT Hart ◽  
AL Ottrey ◽  
M Onda ◽  
...  
Keyword(s):  
Dipole Moment ◽  
Ab Initio ◽  
Bond Length ◽  
Bond Order ◽  
Microwave Spectrum ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Bond Orders ◽  
Bond Lengths ◽  
Typical Error

The microwave spectrum of the benzene isomer 3,4-dimethylenecyclobutene including spectra of all possible single 13C-substituted and sufficient singly and doubly D-substituted species to give a complete r5 geometry, have been measured and analysed. An estimate of the re geometry has also been derived. The additional precise CC bond lengths obtained for an unsubstituted, conjugated hydrocarbon enable us to examine bond order-bond length relationships more thoroughly than has previously been possible. The CC bond lengths exhibit a noticeably better correlation with SCFMO bond orders than with simple H�ckel bond orders. Further confirmatory measurements of the dipole moment of dimethylenecyclobutene have been made. Ab initio molecular orbital calculations using a 6-31G basis set give an optimized geometry with CC bond lengths within 2 pm of the r5 values. The computed dipole moment agrees almost exactly with experiment but a corresponding calculation on fulvene is discrepant with experiment by 0.16 D, which is probably a more typical error.

Theoreticalversusexperimental geometries in S-bridged manganese carbonyl complexes

2003 ◽  
Vol 36 (4) ◽  
pp. 1050-1055 ◽  
Author(s):  
Juan F. Van der Maelen Uría ◽  
Javier Ruiz ◽  
Santiago García-Granda
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Basis Sets ◽  
Medium Size ◽  
Carbonyl Complexes ◽  
X Ray Diffraction ◽  
Bond Lengths ◽  
Hartree Fock ◽  
Experimental Geometry ◽  
Manganese Carbonyl

The experimental geometry obtained from single-crystal X-ray diffraction for a number of binuclear S-bridged manganese complexes is compared with the results of theoretical calculations made at theab initiolevel by using Hartree–Fock and density functional theory methods with medium-size and large basis sets. The optimized geometries obtained were somewhat relaxed when compared with the experimental ones, with very similar bond and torsion angles but longer bond lengths. The mean square deviation for bond lengths (angles) was found to be between 0.046 Å (1.1°) and 0.004 Å (0.7°) depending on the theoretical model used.

Accurate ab initio Calculations of Methane Dimer Interaction Energies and Molecular Dynamics Simulation of Fluid Methane

2009 ◽  
Vol 1177 ◽  
Author(s):  
Arvin Huang-Te Li ◽  
Sheng Der Chao
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Binding Energy ◽  
Ab Initio ◽  
Bond Length ◽  
Dynamics Simulation ◽  
Basis Set ◽  
Basis Sets ◽  
Equilibrium Bond Length ◽  
Basis Size

AbstractIntermolecular interaction potentials of the methane dimers have been calculated for 12 symmetric conformations using the Hartree-Fock (HF) self-consistent theory, the second-order M�ller-Plesset (MP2) perturbation theory, and the coupled-cluster with single and double and perturbative triple excitations (CCSD(T)) theory. The HF calculations yield unbound potentials largely due to the exchange-repulsion interaction. In MP2 and CCSD(T) calculations, the basis set effects on the repulsion exponent, the equilibrium bond length, the binding energy, and the asymptotic behavior of the calculated intermolecular potentials have been thoroughly studied. We have employed basis sets from the Slater-type orbitals fitted with Gaussian functions, Pople�s medium size basis sets to Dunning�s correlation consistent basis sets. With increasing basis size, the repulsion exponent and the equilibrium bond length converge at the 6-31G** basis set and the 6-311++G(2d, 2p) basis set, respectively, while a large basis set (aug-cc-pVTZ) is required to converge the binding energy at a chemical accuracy (˜0.01 kcal/mol). We used the BSSE corrected results that systematically converge to the destined potential curve with increasing basis size. The binding energy calculated and the equilibrium bond length using the CCSD(T) method are close to the results at the basis set limit. For molecular dynamics simulation, a 4-site potential model with sites located at the hydrogen atoms was used to fit the ab initio potential data. This model stems from a hydrogen-hydrogen repulsion mechanism to explain the stability of the dimer structure. MD simulations using the ab initio PES show good agreement on both the atom-wise radial distribution functions and the self-diffusion coefficients over a wide range of experimental conditions.

Sign in / Sign up

Export Citation Format

Share Document