SCF-MO computational analysis of the geometric conformation and charge distribution in picric acid and alkali picrate salts

1996 ◽  
Vol 74 (1) ◽  
pp. 70-78 ◽  
Author(s):  
Zbigniew Zimpel ◽  
Barbara R. Nelson ◽  
John A. Weil
Keyword(s):  
Charge Distribution ◽  
Computational Analysis ◽  
Picric Acid ◽  
Minimum Energy ◽  
Mulliken Charge ◽  
Resonance Effects ◽  
Molecular Electron ◽  
Optimized Model ◽  
Atomic Coordinates ◽  
Density Results

SCF-MO computations were employed in a study of picric acid, the –1 picrate ion, and Li, Na, and K picrates. Atomic coordinates from crystallographic structural analyses were used as initial parameters in the computation of the minimum-energy conformations of each free molecule at the 6-31G level. The Mulliken charge numbers for each atom in the optimized model molecules were calculated at the 6-31G** level. The induction and resonance effects of the OX group (X = H, Li, Na, K) on the trinitrophenyl ring are discussed. It is demonstrated that molecular (electron) isodensity surfaces (MIDCOs) describe charge-density results nicely compatible with the point Mulliken charge numbers. Key words: picrates, SCF-MO, charge distribution.

Electronic Structure and Bonding at the Al-terminated Al(111)/α-Al2O3(0001) Interface: A First Principles Study

2000 ◽  
Vol 654 ◽  
Author(s):  
Donald J. Siegel ◽  
Louis G. Hector ◽  
James B. Adams
Keyword(s):  
First Principles ◽  
Bond Order ◽  
Minimum Energy ◽  
Covalent Character ◽  
Population Analyses ◽  
Bonding Interaction ◽  
Optimized Model ◽  
Α Al2o3 ◽  
Mayer Bond Order ◽  
Atomic Coordinates

AbstractWe have performed ab initio calculations to determine the bonding character of the Al-terminated Al(111)/α-Al2O3(0001) interface. By using an optimized model in which all atomic coordinates were relaxed to their minimum energy positions, we have determined that Al-O bonds constitute the primary interfacial bonding interaction. Our electron localization, Mayer bond order, and Mul- liken population analyses reveal that these bonds are very similar to the cation-anion bonds found in the bulk oxide, and are therefore mainly ionic, with a smaller amount of covalent character. However, there is also evidence of metal-cation bonding across the interface, a result which could be significant to understanding bonding at interfaces with other corundum-like oxides.

Electronic, Vibrational, and Structural Study of Polysaccharide Agar-Agar Biopolymer

2021 ◽  
Vol 33 ◽  
pp. 35-46
Author(s):  
Ankita Pandey ◽  
Abhishek Kumar Gupta ◽  
Shivani Gupta ◽  
Sarvesh Kumar Gupta ◽  
Rajesh Kumar Yadav
Keyword(s):  
Charge Distribution ◽  
Molecular Orbital ◽  
Structural Study ◽  
Density Functional ◽  
Vibrational Analysis ◽  
Chemical Properties ◽  
Atomic Charge ◽  
Dft Method ◽  
Basis Set ◽  
Mulliken Charge

Polysaccharide biopolymer Agar-Agar extracted from red algae is a natural and biodegradable polymer. It is a combination of agarose (a neutral and linear polymer, with repeated units of agarobiose) and a heterogeneous mixture of agaropectin (a charged sulfated polymer). In this study, a comparative study of structural vibrational and electrochemical properties of agar-agar biopolymer with two different methods HF (Hartree-Fock) and DFT (Density Functional Theory) using a basis set 631+G (d, p) is performed. The comparative structural study of agar-agar biopolymer by HF and DFT method has been carried out to calculate the stability of the molecule. The thermionic properties and Mulliken charge distribution are analysed to deliver a quantitative study of partial atomic charge distribution. The overall vibrational analysis of primal modes of the biopolymer has been studied using FTIR analysis. Based on highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) composition and energies, various chemical parameters of the biopolymer have been evaluated. The Physico-chemical properties of this polysaccharide show a strong correlation with its optimized structure. Agar-agar has its application in the electrochemical, biotechnological, and pharmaceutical fields, as a stabilizer and gelling material.

Charge distributions and chemical effects. XLVII. Density matrix contribution to the charge distribution in hydrocarbons, arising from singly excited configurations in CI calculations

1992 ◽  
Vol 70 (1) ◽  
pp. 68-73 ◽  
Author(s):  
Claude Mijoule ◽  
Jean-Marie Leclercq ◽  
Michel Comeau ◽  
Sándor Fliszár ◽  
Maud Picard
Keyword(s):  
Density Matrix ◽  
Charge Density ◽  
Charge Distribution ◽  
Configuration Interaction ◽  
Mulliken Charge ◽  
Charge Distributions ◽  
Chemical Effects ◽  
Net Charges ◽  
Ci Calculations

The involvement of excited configurations in Mulliken charge analyses is examined for ethylene and acetylene, using an optimized 4-31G basis. The net charges of carbon, −346.4 × 10−3 (C2H4) and −335.3 × 10−3 e (C2H2) at the SCF level, are reduced to −269.9 × 10−3 and −271.2 × 10−3 e, respectively. Double excitations appear to contribute little to these corrections. In acetylene, three single σ → σ* type excitations are responsible for ~83% of the charge correction whereas, as expected, the role of π → π* type excitations is small. Similarly, four σ → σ* configurations account for ~76% of the correction in ethylene. These effects are particularly important in comparisons with alkanes, whose charges are relatively little affected by CI corrections. Theoretical charges obtained from CI calculations appear to converge toward their empirical counterparts in a generalization of Mulliken's scheme, which allows for an uneven partitioning of CH overlap populations. Keywords: charge density, configuration interaction.

scholarly journals Corrosion Inhibitive Potentials of some 2H-1-benzopyran-2-one Derivatives- DFT Calculations

2021 ◽  
Vol 11 (6) ◽  
pp. 13968-13981
Keyword(s):  
Charge Distribution ◽  
Metal Surface ◽  
Electrostatic Potential ◽  
Density Functional ◽  
Effective Interaction ◽  
Basis Set ◽  
Mulliken Charge ◽  
Surface Mode ◽  
Adsorption Sites ◽  
Fukui Indices

There is an increased demand for metals and alloys because of their use in household appliances and industrial machines. However, they react with the environment and are consequently prone to loss of strength and durability owing to corrosion. In a bid to eradicate or control this, the use of corrosion inhibitors has been employed. Quantum chemical calculations have been used to predict the corrosion inhibitive potentials of novel molecules and probe into their metals' surface mode of action. Density functional theory was employed here with a polar basis set, 6-31G(d), to investigate the corrosion inhibitive potentials of some 2H-1- benzopyran-2-ones derivatives via their electronic properties, global reactivity descriptors, electrostatic potential maps, and Fukui indices. The energy gaps follow the order: c > e > a > d > b > g > f > h, indicative that compounds f and h would effectively protect metals’ surface against corrosion with the HOMO map essentially delocalized over the benzopyran-2-one moiety and the attached substituents while the LUMO plot shows a delocalization of the lowest vacant molecular orbitals over the entire benzopyran-2-one moiety. The asymmetric charge distribution on the inhibitors from the electrostatic potential maps indicates that each compound possesses reactive adsorption sites for bonding and back-bonding with the metal surface. The Mulliken charge distribution and the Fukui indices reveal that the adsorption of an inhibitor on a metal surface is not only via the heteroatoms like O, Cl, Br, and N. The contribution of carbon atoms as nucleophilic and electrophilic centers ensures effective interaction between a metal surface and the inhibitor and isolates the material from corroding environment.

scholarly journals Energy Minimization

2020 ◽  
Author(s):  
Budhayash Gautam
Keyword(s):  
Energy Minimization ◽  
Minimum Energy ◽  
Electrostatic Energy ◽  
Covalent Bonds ◽  
Energy Accounting ◽  
Energetic State ◽  
Indispensable Tool ◽  
The Given ◽  
Short Contacts ◽  
Atomic Coordinates

The energetic state of a protein is one of the most important representative parameters of its stability. The energy of a protein can be defined as a function of its atomic coordinates. This energy function consists of several components: 1. Bond energy and angle energy, representative of the covalent bonds, bond angles. 2. Dihedral energy, due to the dihedral angles. 3. A van der Waals term (also called Leonard-Jones potential) to ensure that atoms do not have steric clashes. 4. Electrostatic energy accounting for the Coulomb’s Law m protein structure, i.e. the long-range forces between charged and partially charged atoms. All these quantitative terms have been parameterized and are collectively referred to as the ‘force-field’, for e.g. CHARMM, AMBER, AMBERJOPLS and GROMOS. The goal of energy Minimization is to find a set of coordinates representing the minimum energy conformation for the given structure. Various algorithms have been formulated by varying the use of derivatives. Three common algorithms used for this optimization are steepest descent, conjugate gradient and Newton–Raphson. Although energy Minimization is a tool to achieve the nearest local minima, it is also an indispensable tool in correcting structural anomalies, viz. bad stereo-chemistry and short contacts. An efficient optimization protocol could be devised from these methods in conjunction with a larger space exploration algorithm, e.g. molecular dynamics.

Estimation of Resonance Energy from Forced Nonplanar Conformations of Conjugated Molecules

2005 ◽  
Vol 70 (10) ◽  
pp. 1577-1588
Author(s):  
Stanislav Böhm ◽  
Otto Exner
Keyword(s):  
Density Functional ◽  
Classical Model ◽  
Minimum Energy ◽  
Resonance Energy ◽  
Isodesmic Reactions ◽  
Conjugated Molecules ◽  
Functional Theory ◽  
Resonance Effects ◽  
The Density Functional Theory ◽  
Derivatives Of

Energies of 39 derivatives of buta-1,3-diene in the twisted conformation were calculated within the framework of the density functional theory at the B3LYP/6-311+G(d,p) level. By comparing with the same molecules in their natural minimum-energy conformations, a scale of resonance effects of various substituents was obtained and expressed in terms of isodesmic reactions. Comparison with other similar scales revealed that this model is not particularly advantageous, its main shortcoming being the relatively small effect. In any case it confirmed that the scales of resonance effects obtained from different models are only very roughly proportional: the classical model of resonance works well in representative examples but has its clear limitation when unduly extended.

β-K2SO4-Type Isomorphs: Prediction of Structures and Refinement of Rb2CrO4

1998 ◽  
Vol 54 (2) ◽  
pp. 115-120 ◽  
Author(s):  
S. Aleksovska ◽  
S. C. Nyburg ◽  
Lj. Pejov ◽  
V. M. Petrusevski
Keyword(s):  
Chemical Composition ◽  
Crystal Structures ◽  
Structure Determination ◽  
Mulliken Charge ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Related Compounds ◽  
Tetrahedral Anion ◽  
Atomic Coordinates

The crystal structures of members within a group of isostructural compounds may be successfully predicted. This is demonstrated for the β-K2SO4 group isomorphs with the general formula M 2 XO4, which were chosen as a family of very closely related compounds nearly all with accurately refined crystal structures. The unit-cell parameters and the fractional atomic coordinates are shown to exhibit systematic variations with both cation and anion size, as well as the Mulliken charge on the O atom in the tetrahedral anion. This allows the prediction of the crystal structures of members in the series, with only the chemical composition of the compound being known. The agreement is good, except for an early structure determination of Rb2CrO4. The now refined structure gives excellent agreement with that predicted.

Comparison of Theoretical and Experimental Determinations of cis/trans Proline Isomer Ratios: Effect of Molecular Charge State

1989 ◽  
Vol 42 (7) ◽  
pp. 1011 ◽  
Author(s):  
J Bremer ◽  
GL Mendz
Keyword(s):  
Minimum Energy ◽  
Direction Cosine ◽  
Statistical Weight ◽  
Dielectric Constants ◽  
Conformational Energy ◽  
Conformational Energy Calculations ◽  
End Groups ◽  
Molecular Charge ◽  
Theoretical Predictions ◽  
Atomic Coordinates

The resonances of the 1H and 13C n.m.r. spectra of the peptide Pro-Pro-Pro in aqueous solutions have been assigned to specific nuclei by employing one- and two-dimensional techniques and pH titrations. Minimum energy conformations of the tripeptide in different ionization states were estimated by conformational energy calculations with two effective dielectric constants. The cis/trans isomer ratios of the lowest energy conformers obtained for each set of conditions were compared to the isomer ratios measured from the 13C n.m.r. spectra of the peptide in the cationic, zwitterionic and anionic forms. The theoretical predictions did not agree with the experimental data. The conformations and geometry of triprolyl sequences in the uncharged pentapeptide Ac- Gly-Pro-Pro-Pro-Gly-NHMe were investigated for different isomer configurations of the proline residues. The structure of the molecule was characterized by its conformational energy and by two other parameters estimated from the atomic coordinates of each conformation: the distance between atoms located at the end groups, and the direction cosine between vectors defined at the N- and C-terminal ends of the molecule. About 90% of the statistical weight of the lowest energy conformers corresponded to extended geometries of the triprolyl sequence.

Sign in / Sign up

Export Citation Format

Share Document