Quantum mechanics ab initio calculations

A quantum mechanical ab initio calculation using a 3-21G basis set without further geometry optimization (single point calculation) was subsequently performed on all AMI optimized (minimized) conformations using the Spartan program. 

We will limit ourselves here to introducing the simplest of the quantum mechanics procedures the Modified Electron Gas (MEG) treatment of Gordon and Kim (1971). This procedure is on the borderline between the classical atomistic approach and quantum mechanics ab initio calculations that determine energy by applying the variational principle. A short introduction to MEG treatment should thus be of help in filling the conceptual gap between the two theories. 

C. Pisani, Quantum-Mechanical Ab-Initio Calculation of the Properties of Crystalline Materials. Based on the Fourth School of Computational Chemistry of the Italian Chemical Society, held in Torino, Italy, 19-24 September 1994, in Lect. Notes Chem., Vol. 67, Springer, Berlin, 1996. 

There are some articles on solid state FSGO which are as follows 1 -Gaussian orbital calculations of solids. Crystalline lithium hydride. 2-Ab initio Gaussian orbital calculation of the (100) surface of crystalline lithium hydride. 3-Quantum mechanical ab initio calculations of the surface structure of crystalline lithium hydride. 4-Absolute calculation of the adsorption of a hydrogen molecule on the (100) surface of crystalline lithium hydride. ... 

CCI4 + CCI4) were computed using quantum mechanical ab initio calculation. A good agreement was obtained. 

To focus on the influence of water on the chemical activity of gold in nanocatal3dic reactions, quantum mechanical ab initio calculations were performed [396] for model systems that do not exhibit charging effects originating from excess electrons bound to free An clusters (i.e., gold cluster anions) [33,382,397] or from defects at the metal-oxide surface [209,368] that have been shown, as described in the previous subsections, to promote the... 

Several evaluations of Af/7° (HCN, g, 298.15 K) from spectroscopic determinations of the enthalpy of atomisation of HCN(g) and from quantum mechanical ab initio calculations of enthalpies of reactions are available. Martin [96MAR] calculated Af//° (HCN, g, 298.15 K) = (128.24 2.54) kJ-moP from experimental spectroscopic data. From ab initio calculations of the enthalpy of atomisation of HCN(g) at 0 K and the enthalpy of the reaction 2HCN(g) (CN)2(g) + N2(g) he obtained with auxiliary... 

The ring-chain tautomeric equilibria of l-oxa-3,5-diaza-l,3,5-hexatrienes and 2//-l,3,5-oxa-diazines (see Section 6.18.3.1.2.i) have been studied extensively by spectroscopic ( H and C NMR, IR, and UV) methods, and by quantum mechanical ab initio calculations <93CB957>. It is found that... 

It has to be concluded that the bonding character and crystal structure of an inter-metallic can be predicted in a significant way only on the basis of a quantum-mechanical, ab initio calculation for the re-... 

The elastic behavior of NiAl has been studied repeatedly and the elastic moduli have been determined experimentally for polycrystals and single crystals as a function of composition and temperature (Wasilewski, 1966 Rusovic and Warlimont, 1977, 1979 Harmouche and Wolfenden, 1985, 1987). The elastic behavior has also been studied theoretically by quantum-mechanical, ab initio calculations, and the resulting elastic moduli are in close agreement with the experimental values (Yoo et al. 1990 Fu and Yoo, 1992b Freeman etal., 1992 Yoo and Fu, 1993). 

The methods discussed so far are based on the principles of classical mechanics and necessitate the use of experimental data in the parametrization of the potential model chosen. An alternative approach implies that results of quantum mechanical (QM) calculations are employed as such experimental data. Within limits this can allow us to avoid the use of any experimental information other than the values of fundamental physical constants in quantum mechanical ab initio calculations. Alternatively, information about vibrational spectra are also accessible on the direct way from QM calculations. 

Pisani C, Dovesi R, Roetti C (1988) Hartree Fock ab initio treatment of crystalline systems, vol 48. Lecture notes in chemistry. Springer, Berlin Heidelberg New York Pisani C (ed) (1996) Quantum mechanical ab initio calculation of the properties of crystalline materials, vol 67. Lecture notes in chemistry. Springer, Berlin Heidelberg New York... 

Quantum-mechanical ab initio calculations for small molecular systems are widely used these days as an instrument in studying problems in various Helds of chemistry and molecular physics . Most studies deal with ground-state phenomena, i.e. the structure and properties of compounds, thermal reaction pathways and dynamical behavior based on this information. There has been a noticeable increase in excited-state studies in recent years, however, in particular in connection with problems in molecular spectroscopy, in ionization processes or in the detailed study of photochemical reactions, such as photodissociation, energy-transfer and charge-exchange reactions. The calculations are especially powerful for small molecules (for example, for systems up to SO electrons and six atoms other than hydrogen), and hence numerous applications are found in particular in the area of atmospheric and interstellar chemistry and in the study of combustion processes. In these Helds it is often found that experimental and theoretical studies are undertaken in close conjunction and that the two yield complementary data which, taken together, are able to clarify a process. In other instances it is not uncommon that for short-lived species the values obtained from calculations are so far the only ones available. 

Eckl B, Vrabec J, Hasse H (2008) Set of molecular models based on quantum mechanical ab initio calculations and thermodynamic data. J Phys Chem B 112 12710-12721... 

CFT and LFT have a historical background from the end of the 1920s and therefore we should not be surprised if the exact definitions of the two models vary between different textbooks. CFT and LFT together form the background knowledge for all discussions on the electron structure of transition metal systems. They serve to interpret experimental spectra as well as the results of quantum mechanical ab initio calculations. 

Quantum Mechanical ab initio calculations on the prototrope equilibrium between the aminophosphines (phosphazane form) (1) and the iminophosphorane (phosphazene form) (2) (normally shifted to the left), have confirmed that the energy difference is in favour of the former but decreases as the electronegativity of the R substituent is increased from 1.5 to 3, in accord with experimental observations. The calculations also support the mechanism for the formation of polyphosphazene (3) from tris(amino)phosphine (la), via its phosphazene tautomer (2a) (see also Section 3). ... 

Aspects of phosphazene research " and of the history of phosphazenes have been examined. The prototrope equilibrium (Scheme 13) between the polyaminophosphines (NH form) and the polyiminophosphines (polyphosphazene or PH form) has been studied by Quantum Mechanical ab initio calculations. When R = H, the energy difference is in favour of the NH tautomer, but if R = NH2 the more stable is the polyphosphazene form. In fact, the preference for the later increases with the electronegativity of the R substituent, and in agreement with the experimental facts, the calculations showed that the polymerization of the monophosphazanes (1) (see Section 1) should be favourable when the electronegativity of R is about 3. The polyhydrido phosphazene has an helical structure with small bond alternation. The calculations also support the mechanisms for the formation of the polyhydridophosphazene (3) from tris(amino)phosphine P(NH2)3 (la) via its phosphazene (NH2)2HP=NH (2a) tautomer. ... 

Vol. 67 C. Pisani (Ed.), Quantum-Mechanical Ab-initio Calculation of the Properties of Crystalline Materials. VII, 328 pages. 1996. 

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