Comment on "Calculation of nuclear magnetic shieldings using an analytically differentiated relativistic shielding formula" [J. Chem. Phys. 123, 114102 (2005)].
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Comment↗
Biomedical subjects
Pekka Manninen
Publications and source records attributed to Pekka Manninen.
Coupled-cluster theory in a projected atomic orbital basis.
We present a biorthogonal formulation of coupled-cluster (CC) theory using a redundant projected atomic orbital (PAO) basis. The biorthogonal formulation provides simple equations, where the projectors involved in the definition of the PAO basis are absorbed in the integrals. Explicit expressions for the coupled-cluster singles and doubles equations are derived in the PAO basis. The PAO CC equations can be written in a form identical to the standard molecular orbital CC equations, only with integrals that are related to the atomic orbital integrals through different transformation matrices. The dependence of cluster amplitudes, integrals, and correlation energy contributions on the distance between the participating atomic centers and on the number of involved atomic centers is illustrated in numerical case studies. It is also discussed how the present reformulation of the CC equations opens new possibilities for reducing the number of involved parameters and thereby the computational cost.
Journal Article↗
Systematic Gaussian basis-set limit using completeness-optimized primitive sets. A case for magnetic properties.
We discuss the connection between the completeness of a basis set, measured by the completeness profiles introduced by Chong (Can J Chem 1995, 73, 79) at a certain exponent interval, and the possibility of reproducing molecular properties that arise either in the region close to the atomic nuclei or in the valence region. We present a scheme for generating completeness-optimized Gaussian basis sets, in which a preselected range of exponents is covered to an arbitrary accuracy. This is done by requiring Gaussian functions, the exponents of which are selected without reference to the atomic structure, to span the range with completeness profile as close to unity as wanted with as few functions as possible. The initial exponent range can be chosen suitable for calculations of molecular energetics or other valence-like properties. By extending the exponent range, properties requiring augmentation of the basis at a given angular momentum value and/or in a given distance range from the nucleus may be straightforwardly and systematically treated. In this scheme a universal, element-independent exponent set is generated in an automated way. The relation of basis-set completeness and performance in the calculation of magnetizability, nuclear magnetic shielding, and spin-spin coupling is tested with the completeness-optimized primitive sets and literature basis sets.
Algorithms↗
Perturbational calculations of parity-violating effects in nuclear-magnetic-resonance parameters.
We investigate the effects of the parity-violating electroweak interaction in the spectral parameters of nuclear magnetic resonance. Perturbational theory of parity-violating effects in the nuclear magnetic shielding is presented to the order of G(F)alpha, and in the indirect spin-spin coupling, to the order of G(F)alpha3. These leading-order parity-violating corrections are evaluated using analytical linear-response theory methods based on Hartree-Fock and density-functional theory reference states. Parity-violating contributions to spin-spin couplings are evaluated for the first time at the first-principles level. Calculations are carried out for two chiral halomethanes, bromochlorofluoromethane and bromofluoroiodomethane.
Journal Article↗
Leading-order relativistic effects on nuclear magnetic resonance shielding tensors.
We present perturbational ab initio calculations of the nuclear-spin-dependent relativistic corrections to the nuclear magnetic resonance shielding tensors that constitute, together with the other relativistic terms reported by us earlier, the full leading-order perturbational set of results for the one-electron relativistic contributions to this observable, based on the (Breit-)Pauli Hamiltonian. These contributions are considered for the H(2)X (X = O,S,Se,Te,Po) and HX (X = F,Cl,Br,I,At) molecules, as well as the noble gas (Ne, Ar, Kr, Xe, Rn) atoms. The corrections are evaluated using the relativistic and magnetic operators as perturbations on an equal footing, calculated using analytical linear and quadratic response theory applied on top of a nonrelativistic reference state provided by self-consistent field calculations. The (1)H and heavy-atom nuclear magnetic shielding tensors are compared with four component, nearly basis-set-limit Dirac-Hartree-Fock calculations that include positronic excitations, as well as available literature data. Besides the easy interpretability of the different contributions in terms of familiar nonrelativistic concepts, the accuracy of the present perturbational scheme is striking for the isotropic part of the shielding tensor, for systems including elements up to Xe.
Journal Article↗
Perturbational relativistic theory of electron spin resonance g-tensor.
We carry out a complete treatment of the leading-order relativistic one-electron contributions, arising from the Breit-Pauli Hamiltonian, to the g-tensor of electron spin resonance spectroscopy. We classify the different terms and discuss their interpretation as well as give numerical ab initio estimates for the F2(-), Cl2(-), Br2(-), and I2(-) series, using analytical response theory calculations with a multiconfigurational self-consistent field reference state. The results are compared to available experimental data. (c) 2004 American Institute of Physics
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Determination of semivolatile compounds in Baltic herring (Clupea harengus membras) by supercritical fluid extraction-supercritical fluid chromatography-gas chromatography-mass spectrometry.
The on-line supercritical fluid extraction-supercritical fluid chromatography-gas chromatography method was applied to the determination of volatile compounds of raw and baked Baltic herring (Clupea harengus membras). The analytes were extracted with supercritical carbon dioxide at 45 degrees C and 10 MPa pressure. After extraction, the volatiles and coeluted lipids were separated on-line using supercritical fluid chromatography and the volatile fraction was introduced directly into a gas chromatograph. In all, 30 compounds were identified from fish samples with mass spectrometry. The most abundant compounds in the fresh Baltic herrings were heptadecane and 1-heptadecene. When the fish were stored for 3-6 days at 6 degrees C, the total peak area of the volatiles began to increase and the proportions of short chain acids (acetic, propanoic, 2-methylpropanoic, and 3-methylbutanoic) also increased. After 8-9 days of storage, 3-methylbutanoic acid comprised about 36 and 40% of all volatiles in raw and baked herring, respectively.
Acetic Acid↗