scholarly journals Global spectroscopy of the water monomer

2012 ◽  
Vol 370 (1968) ◽  
pp. 2728-2748 ◽  
Author(s):  
Oleg L. Polyansky ◽  
Nikolay F. Zobov ◽  
Irina I. Mizus ◽  
Lorenzo Lodi ◽  
Sergei N. Yurchenko ◽  
...  
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Configuration Interaction ◽  
Basis Set ◽  
Maximum Deviation ◽  
High Resolution Spectrum ◽  
Dissociation Limit ◽  
Relativistic Energy ◽  
Interaction Technique ◽  
Semi Empirical

Given the large energy required for its electronic excitation, the most important properties of the water molecule are governed by its ground potential energy surface (PES). Novel experiments are now able to probe this surface over a very extended energy range, requiring new theoretical procedures for their interpretation. As part of this study, a new, accurate, global spectroscopic-quality PES and a new, accurate, global dipole moment surface are developed. They are used for the computation of the high-resolution spectrum of water up to the first dissociation limit and beyond as well as for the determination of Stark coefficients for high-lying states. The water PES has been determined by combined ab initio and semi-empirical studies. As a first step, a very accurate, global, ab initio PES was determined using the all-electron, internally contracted multi-reference configuration interaction technique together with a large Gaussian basis set. Scalar relativistic energy corrections are also determined in order to move the energy determinations close to the relativistic complete basis set full configuration interaction limit. The electronic energies were computed for a set of about 2500 geometries, covering carefully selected configurations from equilibrium up to dissociation. Nuclear motion computations using this PES reproduce the observed energy levels up to 39 000 cm −1 with an accuracy of better than 10 cm −1 . Line positions and widths of resonant states above dissociation show an agreement with experiment of about 50 cm −1 . An improved semi-empirical PES is produced by fitting the ab initio PES to accurate experimental data, resulting in greatly improved accuracy, with a maximum deviation of about 1 cm −1 for all vibrational band origins. Theoretical results based on this semi-empirical surface are compared with experimental data for energies starting at 27 000 cm −1 , going all the way up to dissociation at about 41 000 cm −1 and a few hundred wavenumbers beyond it.

Conformational Structure of Chloromethyldichlorophosphines

2002 ◽  
Vol 57 (6-7) ◽  
pp. 333-336
Author(s):  
Evgenii A. Romanenko ◽  
Alexander M. Nesterenko
Keyword(s):  
Experimental Data ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Electron Correlation ◽  
Basis Set ◽  
Conformational Structure ◽  
Gauche Conformation ◽  
Nuclear Quadrupole ◽  
Set Up ◽  
Good Agreement

IThe 35Cl nuclear quadrupole resonances (77 K) and ab initio calculations of trichloromethyldichlorophosphine () show that it exists in the chess conformation form. The barrier to internal rotation about the P-C bond in I at the RHF/6-31++ G(d,p) level equals to 38.1 kJ mol-1. In chloromethyldichlorophosphine (II) the extension of the basis set up to the RHF/6-311++G(df, pd) level does not improve the description of the most preferable gauche-conformation; only if electron correlation (at the MP2 level) is taken into account the results are in a good agreement with experimental data.

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.

Turbocharger Performance Maps Building Using a Hot Gas Test Stand

2008 ◽  
Author(s):  
Giuliano Gardolinski Venson ◽  
Jose´ Eduardo Mautone Barros
Keyword(s):  
Experimental Data ◽  
Empirical Model ◽  
Quadratic Equation ◽  
Test Stand ◽  
Experimental Methodology ◽  
Maximum Deviation ◽  
Gas Generator ◽  
Hot Gas ◽  
Model Based ◽  
Semi Empirical

This work presents the experimental methodology used in turbochargers tests using a hot gas test stand. The test consists in recording the characteristic curves of the turbochargers, known as flow maps or performance maps. A tubular combustion chamber, designed to operate burning gaseous fuels, is used to drive the set. By using a hot gas generator it’s possible to simulate the real operational condition of the turbine. The experimental configuration allows reproducing the self-sustained turbocharger operation. The test stand instrumentation is based on virtual instrumentation, where acquisition of the sensors and control are made by computer. For the performance maps obtainment, the experimental data are treated through an empirical model based in a quadratic equation involving two variables, mass flow rate and rotational speed. The results present the performance and efficiency maps for the APL-240 Master Power turbocharger, used in commercial heavy trucks. With the results is made a comparison between the experimental maps with the maps gotten through a semi-empirical model based in modified Euler equation. The maximum deviation for compressor and turbine semi-empirical pressure ratios are respectively 8% and 14% in relation to the experimental data.

scholarly journals Computational study of the rovibrational spectrum of H2O-HF

2021 ◽  
Author(s):  
Dominika VIGLASKA ◽  
Xiao-Gang Wang ◽  
Tucker CARRINGTON ◽  
David Tew
Keyword(s):  
Experimental Data ◽  
Potential Energy ◽  
Potential Energy Surface ◽  
Ab Initio ◽  
Energy Surface ◽  
Computational Study ◽  
Energy Levels ◽  
Dissociation Limit ◽  
Lanczos Algorithm ◽  
Vibrational States

In this paper we report rovibrational energy levels, transition frequencies, and intensities computed for H2O-HF using a new ab initio potential energy surface and compare with available experimental data. We use the rigid monomer approximation. A G4 symmetry-adapted Lanczos algorithm and an uncoupled product basis are employed. The rovibrational levels are computed up to J = 4. The new analytic 9-D potential is �t to 39771 counterpoise corrected CCSD(T)(F12*)/augcc- pVTZ energies and reduces to the sum of uncoupled H2O and HF potentials in the dissociation limit. On the new potential better agreement with experiment is obtained by re-assigning the R(1) transitions of two vibrational states.

The ab initio Calculation of Nuclear Quadrupole Coupling Constants with Special Reference to 33S

1992 ◽  
Vol 47 (1-2) ◽  
pp. 203-216 ◽  
Author(s):  
Michael H. Palmer
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Ab Initio Calculation ◽  
Coupling Constants ◽  
Basis Set ◽  
Equilibrium Geometry ◽  
Relaxation Methods ◽  
Quadrupole Coupling ◽  
Nuclear Quadrupole ◽  
The Relationship

AbstractThe ab initio calculation of 33S nuclear quadrupole coupling constants (NQCC) for a range of S-containing compounds with S2, S4 and S6 bonding types is described. All of the calculations used a triple zeta valence + polarisation basis set (TZVP) of gaussian type orbitals; all of the molecules were studied at the TZVP equilibrium geometry. The electric field gradients (EFG) calculated were correlated with the experimental NQCC obtained by either microwave spectroscopy (MW), nuclear quadrupole resonance (NQR) or NMR relaxation methods; although the experimental data cover a wide diversity of chemical types over a long period of time, the slope of the relationship between the EFG (qii) and the NQCC (χii) yields a value for the 33S atomic quadrupole moment of - 0.064 barn, very close to recent calculations with a large atomic basis set, and to experimental data. The relationship between the EFG tensor components and the internal molecular structure features is discussed for a diverse series of molecules.

A Theoretical Structure Study Infrared Spectra of C60O Isomers Through Ab Initio Method

2011 ◽  
Vol 2 (1) ◽  
Author(s):  
Rashid Nizam ◽  
S. Mahdi A. Rizvi ◽  
Ameer Azam
Keyword(s):  
Ab Initio ◽  
Infrared Spectra ◽  
Structure Study ◽  
Basis Set ◽  
Ab Initio Method ◽  
Single Experiment ◽  
Theoretical Structure ◽  
Semi Empirical ◽  
Isomeric Structures ◽  
Neglect Of Differential Overlap

The infrared spectra of C60O isomers have been calculated through ab initio method. It has been observed that the simulated spectrum of one of C60O isomers is matching with the available experimental data in literature, while the other isomers are not matching so much. One can easily understand the basic physical properties of C60O by knowing of their vibration and geometric structures with their interrelation between these properties. It is found that the isomeric structures of C60O are very sensitive to electron correlation treatment with basis set that are employed. So the structure of C60O will not calculate from semi-empirical methods such as modified neglect of differential overlap (MNDO) or AM1 for more accuracy. The simulated spectra show different bands that rarely found all bands simultaneously in single experiment.

The electronic structures, geometries, and relative energies of some N2H2 and N2H2+ systems

1977 ◽  
Vol 55 (2) ◽  
pp. 350-354 ◽  
Author(s):  
N. Colin Baird ◽  
David A. Wernette
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Configuration Interaction ◽  
Electronic Structures ◽  
Ground States ◽  
Heat Of Formation ◽  
Ionization Potentials ◽  
Basis Set ◽  
Relative Stabilities ◽  
Positive Ions

Ab initio calculations using the 4-31G basis set and extensive configuration interaction are reported for the 1Ag state of trans-diimide (1), the 3A″ and 1A1 states of 1,1-dihydrodiazine (2), and the ground states of the positive ions of these systems and of cis-diimide. In all cases the geometries have been optimized. The relative stabilities of these systems are discussed, with particular reference to the heat of formation of trans-1 and to the ionization potentials of 1 and 2.

scholarly journals Geometria de equilíbrio da molécula de Azadiracthin através de métodos semiempíricos e Ab initio em comparação com os dados experimentais fornecidos pela difração de raios X

2017 ◽  
Vol 41 (1) ◽  
pp. 94
Author(s):  
Daniel Augusto Barra de Oliveira ◽  
Yagly G. dos Santos Gomes
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Computational Cost ◽  
Empirical Method ◽  
Biological Applications ◽  
X Ray ◽  
Energetic State ◽  
Semi Empirical ◽  
Equilibrium Geometries ◽  
Data Reproducibility

The azadiracthin is a molecule with many biological applications in the pest control and in the treatment of human diseases. For this reason the geometry study of this molecular structure is essential to understand the biochemical process which it is involved. The study of equilibrium geometries was performed with the aid of quantum mechanics approach that can determine the structures with the least energetic state. The importance of this kind of study is verified when there is experimental data reproducibility by quantum calculations. In this work it was performed calculations of electronic structure with different approaches in order to try reproducing the experimental data base in X ray. The PM6 semi-empirical method was that showed the highest reproducibility of the experimental data. This result optimized yet the relation between computational cost and the good data reproducibility, because it is known that the PM6 semi-empirical method has the computationally less cost that the ab initio approaches that were used in this study. 

Assignment of the UV-Photoelectron Spectrum of Tetrasulfur Tetranitride

1983 ◽  
Vol 38 (3) ◽  
pp. 378-382 ◽  
Author(s):  
M. H. Palmer
Keyword(s):  
Ab Initio ◽  
Configuration Interaction ◽  
Photoelectron Spectrum ◽  
Basis Set ◽  
Koopmans Theorem ◽  
Configuration Interaction Calculations

Abstract Ab initio configuration interaction calculations of the ground and doublet states of S4N4 show changes in the order of states relative to a large basis set Koopmans’ Theorem order. Consequential changes in the assignment of the UV-photoelectron spectrum are reported.

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