AB INITIO CALCULATIONS OF INTERMOLECULAR INTERACTION POTENTIALS OF FULLERENE-FRAGMENTS SYSTEMS

2005 ◽  
Vol 04 (01) ◽  
pp. 49-58 ◽  
Author(s):  
YUKIUMI KITA ◽  
KEI WAKO ◽  
ISAMU OKADA ◽  
MASANORI TACHIKAWA
Keyword(s):  
Ab Initio ◽  
Intermolecular Interaction ◽  
Correlation Energy ◽  
Basis Set ◽  
Basis Sets ◽  
Cubic Phase ◽  
Molecular Orbital Calculations ◽  
Interaction Potentials ◽  
Basis Set Superposition Error ◽  
Intermolecular Distances

We have performed the ab initio molecular orbital calculations for combinations of the fullerene-fragments as the models of the nonbonding interaction of C 60 dimer at the preferred configurations in the simple cubic phase. The intermolecular interaction potentials have been calculated using several basis sets with MP2 level of the electron correlation energy and the basis set superposition error correction. The strong dispersion attractions that is dominant in the van der Waals interaction has been found for the combinations of the fullerene-fragments. The equilibrium intermolecular distances obtained are in good agreement with the corresponding experimental value. The repulsive region of the intermolecular interaction calculated by ab initio method is found to be express by an atom–atom interaction potential with an anisotropic exponential type repulsive term, which is less steep than the conventional Lennard–Jones type potential.

Counterpoise-Corrected Potential Energy Surfaces of Simple Hydrogen-Bonded Systems

1998 ◽  
Vol 63 (9) ◽  
pp. 1343-1354 ◽  
Author(s):  
Pavel Hobza ◽  
Zdeněk Havlas
Keyword(s):  
Potential Energy Surfaces ◽  
Correlation Energy ◽  
Linear Structure ◽  
Water Dimer ◽  
Basis Set ◽  
Basis Sets ◽  
Basis Set Superposition Error ◽  
Gradient Optimization ◽  
Intermolecular Distances ◽  
Hydrogen Bonded

Geometric and energetic characteristics of various simple hydrogen-bonded complexes (water dimer, hydrogen fluoride dimer, formamide dimer, formic acid dimer, glycine dimer) have been studied by gradient optimization, which a priori eliminates the basis set superposition error (BSSE) by using the counterpoise (CP) method, as well as by the standard gradient optimization. Calculations were done at the Hartree-Fock, correlated MP2 and DFT levels with small- and medium-basis sets. The CP-corrected and standard PESs differ, depending on the theoretical level used. Larger differences were found if the correlation energy was included. Intermolecular distances from the CP-corrected PES are consistently longer, and the respective difference may be significant (≈0.1 A). The stabilization energies obtained from the CP-corrected PES are always larger than those from the standard PES. Optimization at the standard PES might result in a wrong structure. For example, the "quasi-linear" structure of the (HF)2 (global minimum) does not exist at the standard MP2/6-31G** and DFT/B3LYP/6-31G** PESs and it is found only when passing to the respective CP-corrected PESs.

Structures of simple anions from ab initio molecular orbital calculations

1976 ◽  
Vol 29 (8) ◽  
pp. 1635 ◽  
Author(s):  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Limited Information ◽  
Orbital Theory ◽  
Comparable Quality ◽  
Split Valence ◽  
Theoretical Results

Ab initio molecular orbital theory with the minimal STO-3G and split-valence 4-31G basis sets is used to obtain geometries of 18 anions:OH-, NH2-, HF2-, BH4-, BF4-, C22-, CN-, NCN2-, N3-, NO2-, NO3-, 0CCO2-, CO32-, HCOO-, CH3COO-, C2O42-, C4O42- and C(CN)3-. The theoretical results are compared with experimental results from the literature. The STO-3G basis set performs somewhat worse for anions than for neutral molecules. On the other hand, the 4-31G basis set gives good results and predicts bond lengths to within 0.02� for all the molecules considered. Limited information on bond angle predictions suggests that these are of comparable quality to those for neutral molecules. The tricyanomethanide ion is predicted to be planar.

scholarly journals CONFORMATIONAL EQUILIBRIUM AND SPECTROSCOPIC PROPERTIES OF CALIX[4]ARENE: THEORETICAL STUDY USING AB INITIO METHOD

2010 ◽  
Vol 8 (3) ◽  
pp. 397-403 ◽  
Author(s):  
Hanggara Sudrajat ◽  
Ria Armunanto
Keyword(s):  
Ab Initio ◽  
Conformational Equilibrium ◽  
Spectroscopic Properties ◽  
Molecular Structures ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Stable Conformer ◽  
Hartree Fock ◽  
Partial Cone

Molecular structures were optimized for the calix[4]arene by ab initio method at the Hartree-Fock level of theory using LANL2DZ and 6-311G basis sets. Conformational equilibrium of four calix[4]arene conformers are reported. The results are compared with experiment, force field, and semiempirical molecular orbital calculations. General trends in relative stabilities of calix[4]arene decrease in following order: cone > partial-cone > 1,2-alternate > 1,3-alternate. The most stable conformer is the cone conformer that is stabilized by an array of four hydrogen bonds and these results agree with the reported experimental observations. All structures were analyzed using theoretical IR, UV-Vis, and 1H NMR spectra attributed to the conformational equilibrium at the Hartree-Fock level of theory using LANL2DZ basis set.     Keywords: ab initio calculation, calix[4]arene, conformations, cone

Ab initio MO Optimizations of Osmiumtetracarbonyldihydride and Metallacyclophanes with two Osmium Atoms and their Molecular Complexes with Different Guests

1998 ◽  
Vol 53 (10) ◽  
pp. 1223-1235
Author(s):  
Inge Warttmann ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Cyano Group ◽  
Single Point ◽  
Molecular Complexes ◽  
Basis Set ◽  
Basis Sets ◽  
Basis Set Superposition Error ◽  
Hartree Fock ◽  
Surprising Effect

AbstractAb initio Hartree-Fock (HF) and density functional (DFT) optimizations on the test m olecule osmiumtetracarbonyldihydride (13) with various basis sets show that the lanl2mb pseudopotential basis set for osmium leads in the HF approximation to more reliable molecular geometries than the DFT calculations. This HF procedure was used for the optimizations of molecular geometries of three isomeric 4,4,4,4,17,17,17,17-octacarbonyl-4,17-diosma[7.7]ortho-, meta- and paracyclophanes 1 to 3, of which 3 was found to be predestined for formation of various host-guest complexes with possible guests benzene (4), fluorobenzene (5), 1,3,5- trifluorobenzene (6), 1,2,4,5-tetrafluorobenzene (7), hexafluorobenzene (8), fluoroanil (9), tetrafluoroethene (10), tetracyanoethene (11) and aniline (12). Results of optimized hostguest geometries are presented graphically for inclusions and associations of guest 4 to 12 with 3. Calculated lanl2mb interaction energies, after correction for basis set superposition error (BSSE), remain favourable only for inclusion of 5 and associations of 5, 10, 11 and 12. Additionally lanl2dz single point calculations for inclusion, which may not need BSSE correction because of the improved basis set, are favourable for 6 and 12. According to lanl2mb HOMO and LUMO energies, 3 may as well easily donate or accept electrons. This may be an interpretation to the surprising effect, that Mulliken total charges are positive on the electron accepting guest molecules 4 to 11. There are geometrical peculiarities in the optimized host-guest complexes for inclusion and association. Fluorine atoms of 5 to 10 and nitrogen atoms of a cyano group of 11 and the amino group of 12 like to come close to one or two carbonyl groups. Similar distances of 2.70 Å to 3.57 Å between the O atom of the carbonyl group and the F atom or N atom appear in all optimizations of inclusion and association of 5 to 12 except in the case of association of tetrafluoroethene (10).

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

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.

A density functional approach toward structural features and properties of C20…N2X2 (X = H, F, Cl, Br, Me) molecules

2014 ◽  
Vol 13 (04) ◽  
pp. 1450023 ◽  
Author(s):  
Reza Ghiasi ◽  
Morteza Zaman Fashami ◽  
Amir Hossein Hakimioun
Keyword(s):  
Density Functional ◽  
Chemical Shifts ◽  
Geometry Optimization ◽  
Structural Features ◽  
Nbo Analysis ◽  
Basis Set ◽  
Basis Sets ◽  
Basis Set Superposition Error ◽  
Homo And Lumo ◽  
Lowest Unoccupied Molecular Orbitals

In this work, the interaction of C 20 with N 2 X 2 ( X = H , F , Cl , Br , Me ) molecules has been explored using the B3LYP, M062x methods and 6-311G(d,p) and 6-311+G(d,p) basis sets. The interaction energies (IEs) obtained with standard method were corrected by basis set superposition error (BSSE) during the geometry optimization for all molecules at the same levels of theory. It was found C 20… N 2 H 2 interaction is stronger than the interaction of other N 2 X 2 ( X = F , Cl , Br , Me ) with C 20. Highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively) levels are illustrated by density of states spectra (DOS). The nucleus-independent chemical shifts (NICSs) confirm that C 20… N 2 X 2 molecules exhibit aromatic characteristics. Geometries obtained from DFT calculations were used to perform NBO analysis. Also, 14 N NQR parameters of the C 20… N 2 X 2 molecules are predicted.

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