| 1. |
- Cappelli, Chiara, et al.
(author)
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The molecular electric quadrupole moment and electric field gradient induced birefringence (Buckingham effect) of Cl2
- 2004
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In: Journal of Computational Methods in Sciences and Engineering. - 1472-7978 .- 1875-8983. ; 4:3, s. 365-380
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Journal article (peer-reviewed)abstract
- An ab initio investigation of the molecular properties rationalizing the electric-field-gradient induced birefringence (Buckingham effect) for Cl_2 is presented. The quadrupole moment is determined using hierarchies of basis sets and wavefunction models. The electric dipole polarizability, the dipole - dipole - quadrupole and dipole - dipole - magnetic dipole hyperpolarizabilities are determined exploiting a Coupled Cluster Singles and Doubles (CCSD) response approach. The properties are zero-point vibrationally averaged, and the contribution of excited ro-vibrational states accounted for. To this end, the interatomic ^1Σ_g^+ ground state potential has been computed at CCSD plus perturbative triples - CCSD(T) - level employing a large augmented correlation consistent basis set. The effect of relativity is estimated at the Dirac-Hartree-Fock level. Our best value for the quadrupole moment of Cl_2 is (2.327 ± 0.010) au and it is in excellent agreement with experiment which, after revision and dependent on the procedure employed for correcting the original estimate of (2.24 ± 0.04) au of Graham et al., [Mol. Phys., 93, 49, (1998)], ranges from (2.31 ± 0.04) au to (2.36 ± 0.04) au.
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| 2. |
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| 3. |
- Ferrighi, Lara, et al.
(author)
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Density-functional-theory study of the electric-field-induced second harmonic generation (EFISHG) of push-pull phenylpolyenes in solution
- 2006
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 425:4-6, s. 5593-5603
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Journal article (peer-reviewed)abstract
- Density-functional theory and the polarizable continuum model have been used to calculate the electric-field-induced second harmonic generation of a series of push-pull phenylpolyenes in chloroform solution. The calculations have been performed using both the Becke 3-parameter Lee-Yang-Parr functional and the recently developed Coulomb-attenuated method functional. Solvation has been investigated by examining the effects of the reaction field, non-equilibrium solvation, geometry relaxation, and cavity field. The inclusion of solvent effects leads to significantly better agreement with experimental observations.
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| 4. |
- Frecus, Bogdan
(author)
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Theoretical studies of EPR parameters of spin-labels incomplex environments
- 2013
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Doctoral thesis (other academic/artistic)abstract
- This thesis encloses quantum chemical calculations performed in the framework of density functional response theory for evaluating electron paramagnetic resonance (EPR) spin Hamiltonian parameters of various spin-labels in different environments. These parameters are the well known electronic g-tensor and the nitrogen hyperfine coupling constants, which are extensively explored in this work for various systems. A special attention was devoted to the relationships that form between the structural and spectroscopic properties that can be accounted for as an environmental inuence. Such environmental effects were addressed either within a fully quantum mechanical formalism, involving simplified model structures that still capture the physical properties of the extended system, or by employing a quantum mechanics/molecular mechanics (QM/MM) approach. The latter implies that the nitroxide spin label is treated quantum mechanically, while the environment is treated in a classical discrete manner, with appropriate force fields employed for its description. The state-of- the art techniques employed in this work allow for an optimum accounting of the environmental effects that play an important role for the behaviour of EPR properties of nitroxides spin labels. One achievement presented in this thesis includes the first theoretical con_rmation of an empirical assumption that is usually made for inter-molecular distance measurement experiments in deoxyribonucleic acid (DNA), involving pulsed electron-electron double resonance (PELDOR) and site-directed spin labeling (SDSL) techniques. This refers to the fact that the EPR parameters of the spin-labels are not affected by their interaction with the nucleobases from which DNA is constituted. Another important result presented deals with the inuence of a supramolecular complex on the EPR properties of an encapsulated nitroxide spin-label. The enclusion complex affects the hydrogen bonding topology that forms around the R2NO moiety of the nitroxide. This, on the other hand has a major impact on its structure which further on governs the magnitude of the spectroscopic properties. The projects and results presented in this thesis offer an example of successful usage of modern quantum chemistry techniques for the investigation of EPR parameters of spin-labels in complex systems.
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| 5. |
- Kula, Mathias, et al.
(author)
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Ab initio study of the magneto-optical rotation of diastereoisomers
- 2008
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In: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 9:3, s. 462-469
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Journal article (peer-reviewed)abstract
- Experimental studies on the natural optical activity and Faraday rotation of the three different stereoisomers of tartaric acid were reported recently by Ruchon et al. [Chem. Phys., Lett. 2005, 412, 411]. The authors noted that the Faraday rotation of the meso (R,S) system differed from those of the (S,S) and (R,R) enantiomers, and derived a simple dipole-dipole interaction model to describe what they claim to be a "new property". We present the results of both density functional theory (DFT) and coupled cluster calculations for a structurally elementary model system composed of two chiral carbon atoms presenting three diastereoisomers (C2H2Cl2F2), as well as a detailed DFT study of the natural and magnetic-field-induced optical rotation of tartaric acid. The effects of electron correlation, basis set, and conformational flexibility are analyzed. It is found that the specific Faraday rotations of the chiral (R,R) and mesa forms of tartaric acid (for lambda = 632.8 nm) differ by about 3%, a value which is quite close In magnitude-but of opposite sign-to that obtained with the simplified model proposed by Ruchon and co-workers.
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