scholarly journals THE INTERACTION OF Co2+-AMMONIA MODELLING: THE COMPARATIVE STUDY BETWEEN AB INITIO AND ELECTRON CORRELATION METHODS

2010 ◽  
Vol 2 (2) ◽  
pp. 67-73
Author(s):  
Harno Dwi Pranowo ◽  
Foliatini Foliatini ◽  
Karna Wijaya
Keyword(s):  
Charge Transfer ◽  
Comparative Study ◽  
Electron Correlation ◽  
Transfer Effect ◽  
Basis Set ◽  
Basis Sets ◽  
Complex Energy ◽  
Hartree Fock ◽  
Correlation Methods ◽  
The Comparative Study

Research on comparison between Hartree-Fock method and electron correlation methods as well as the effect of size of basis sets on representing interaction of Co2+-NH3 observed from complex energy parameters and optimum geometric parameters have been carried out.The first step is screening basis sets based on charge transfer effect and BSSE value. The selected basis set does not yield charge transfer at 1,4 Å  

Calculation of the solvation state of organolithium compounds: Effects of basis sets and electron correlation methods

2009 ◽  
Vol 109 (1) ◽  
pp. 34-42 ◽  
Author(s):  
Lawrence M. Pratt ◽  
Darrel Jones ◽  
Andrea Sease ◽  
Donta Busch ◽  
Emmanuel Faluade ◽  
...  
Keyword(s):  
Electron Correlation ◽  
Basis Sets ◽  
Solvation State ◽  
Organolithium Compounds ◽  
Correlation Methods

Intermolecular Effects on Third Order Nonlinear Optical Properties

1992 ◽  
Vol 247 ◽  
Author(s):  
D. S. Dudis ◽  
A. T. Yeates ◽  
H. A. Kurtz
Keyword(s):  
Optical Properties ◽  
Intermolecular Interactions ◽  
Nonlinear Optical ◽  
Basis Set ◽  
Basis Sets ◽  
Intermolecular Potential ◽  
Correlation Effects ◽  
Third Order ◽  
Hartree Fock ◽  
Intermolecular Contacts

ABSTRACTHartree-Fock ab initio calculations have been used to examine the magnitude of non-polar intermolecular interactions on polarizabilities and second hyperpolarizabilities. In the present case two ethylene molecules were examined in a cofacial interaction. Basis set requirements and correlation effects were considered in deriving the intermolecular potential. Two basis sets were considered for the intermolecular interactions at the Hartree-Fock level, while one set of calculations was performed with corrections for correlation. It is found that intermolecular contacts at the van der Waals distance has little effect on the molecular second hyperpolarizability, but it is not clear what the effect would be for longer oligomers.

scholarly journals A Statistically Supported Antioxidant Activity DFT Benchmark—The Effects of Hartree–Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5058
Author(s):  
Maciej Spiegel ◽  
Andrzej Gamian ◽  
Zbigniew Sroka
Keyword(s):  
Density Functional ◽  
Optimal Level ◽  
Basis Set ◽  
Basis Sets ◽  
Linear Regression Models ◽  
Functional Theory ◽  
Hartree Fock ◽  
Diffuse Function ◽  
Vertical Electron Affinity ◽  
High Level

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage—a challenge we tackle in this study. Eleven DFT functionals with varied Hartree–Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak’s theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06–2X/6–311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.

Effect of Basis Sets on the Selection of the Level of Theory Toward the Development of Quantum-Based Force Field Equation for Ionic Liquids

2005 ◽  
Vol 5 (2) ◽  
pp. 156 ◽  
Author(s):  
A. N. Soriano ◽  
B. T. Doma, Jr.
Keyword(s):  
Ionic Liquids ◽  
Field Equation ◽  
Volatile Organic Compounds ◽  
Force Field ◽  
Organic Compounds ◽  
Basis Set ◽  
Basis Sets ◽  
Hartree Fock ◽  
Volatile Organic ◽  
Selection Of

The chemical industry is under considerable pressure to replace many of the volatile organic compounds. Volatile organic compounds are a major contributor to air pollution, but out of necessity, they are still frequently used in many chemical and industrial processes. A new class of solvents, referred to as ionic liquids, may offer at least a partial solution to the pollution problem caused by volatile organic compounds. Ionic liquids are generally considered "green" solvents because of their environment-friendly properties. However, the main problem that hinders the chemical industry from using ionic liquids is that, compared to conventional organic solvents, relatively little is known about their thermodynamic and transport properties. Since there are large possible combinations of ionic liquids, it would be very expensive if the study were conducted in the laboratory. The more appropriate approach in studying the properties of ionic liquids is to engage in a computational method, which uses a computer software that evaluates ionic liquids' thermophysical quantities via quantum mechanical and molecular mechanical simulations. In this study, a computer simulation, with the aid of SPARTAN '02 software, is used to study the effect of basis sets on the selection of the appropriate level of theory, which would be employed later in developing a quantum-based force field equation for predicting the properties of ionic liquids. Using the Hartree-Fock self-consistent filled (HF-SCF) molecular orbital model with different basis sets, a single point energy calculations were carried out for the chosen ionic liquid. With the exception of the minimal basis set, the SCF total energies for the other basis sets agree with each other in terms of magnitude. The SCF total energy is not affected as the basis set varies from minimal to split valence and as it polarizes. The most appropriate basis set was found to be 6-31G*. Keywords: Basis sets, Hartree-Fock, ionic liquids, force field equation, level of theory, and SPARTAN '02.

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. �

scholarly journals Quantum Mechanical Study of YTiO3 to the Investigation of Piezoelectricity

2011 ◽  
Vol 2011 ◽  
pp. 1-5
Author(s):  
Raimundo Dirceu de Paula Ferreira ◽  
Marcos Antonio Barros dos Santos ◽  
Maycon da Silva Lobato ◽  
Jardel Pinto Barbosa ◽  
Marcio de Souza Farias ◽  
...  
Keyword(s):  
Total Energy ◽  
Piezoelectric Properties ◽  
Piezoelectric Effect ◽  
Basis Set ◽  
Basis Sets ◽  
Gaussian Basis Sets ◽  
Hartree Fock ◽  
Generator Coordinate ◽  
Mechanical Study ◽  
Quantum Mechanical Study

In previous articles we reported through theoretical studies the piezoelectric effect in BaTiO3, SmTiO3, and YFeO3. In this paper, we used the Douglas-Kroll-Hess (DKH) second-order scalar relativistic method to investigate the piezoelectricity in YTiO3. In the calculations we used the [6s4p] and [10s5p4d] Gaussian basis sets for the O (3P) and Ti (5S) atoms, respectively, from the literature in combination with the (30s21p16d)/[15s9p6d] basis set for the Y (3D) atom, obtained by generator coordinate Hartree-Fock (GCHF) method, and they had their quality evaluated using calculations of total energy and orbital energies (HOMO and HOMO-1) of the 2TiO+1 and 1YO+1 fragments. The dipole moment, the total energy, and the total atomic charges in YTiO3 in Cs space group were calculated. When we analyze those properties we verify that it is reasonable to believe that YTiO3 does not present piezoelectric properties.

An approximate ab initio method based on the DIM model

2000 ◽  
Vol 78 (12) ◽  
pp. 1575-1586 ◽  
Author(s):  
John M Cullen
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Electron Correlation ◽  
Correlation Energy ◽  
Basis Sets ◽  
Ab Initio Method ◽  
First Order ◽  
Hartree Fock ◽  
Modified Method ◽  
Electron Correlation Energy

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the Hartree–Fock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the Hartree–Fock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempirical.

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