Theoretical studies on the ionization potential of interacting atoms at large separations

The theory of the one-particle Green's function is applied to calculations of the ionization potential of interacting atoms which are at large separations. Equations for the ionization potential involve terms which relate to Van der Waals interactions between separated atoms and long-range interactions between an atom and an ion. Numerical calculations of the ionization potential of two hydrogen atoms and two helium atoms at large separations are performed. Applications to the ionization potentials of weakly-interacting Van der Waals molecules (NeAr, NeKr, NeXe) are also reported.     

A Green's function approach to the photoelectron spectrum of bis(π-allyl)nickel[1]

The vertical ionization potentials of bis(-allyl)nickel (see (1) in Fig. 1) are calculated by means of the Green's function approach within a semiempirical INDO extension to the first transition metal series. The computed ionization potentials are in good agreement with an experimentally deduced assignment. In contrast to earlier theoretical and experimental studies, the 7a _u () level is predicted on top of the levels corresponding to the Ni 3d orbitals. Our approach leads to a complete assignment of the PE spectrum of (1) in the outer valence region.     

Electron affinities, excitation energies and ionization potentials of the transition metals (I) Sc and Ti

The electron affinities of the Sc and Ti atoms have been obtained by configuration interaction calculations. Energy convergence with respect to the systematic expansion of both the one-electron basis set and the configuration space was investigated for valence electrons, and the inclusion of correlation contributions from core electrons and relativistic effects gave the electron affinities of 0.181 eV and 0.163 eV for Sc and Ti, respectively. These are in excellent agreement with the observed values of 0.189 ± 0.020 eV and 0.080 eV. The same approach was applied for the first excited states and positive ions of both atoms. Excellent agreement with the experimental results was also obtained for these states. Received: 16 February 1998 / Accepted: 2 April 1998 / Published online: 23 June 1998     

Molecular interactions in a homogeneous electric field: the (HF)2 complex

Summary The interaction energy of two HF molecules, subjected to a static external field, is analyzed. The analysis aims at the elaboration of simple expressions able to reproduce environmental and substitution effects on noncovalent molecular interactions.     

Complete basis set, the MP2 ab initio, and hybrid density functional theory evaluation of ionization potential and electron affinity for PH, PH2, PHF, PF, and PF2

A systematic study was performed on the small molecular systems built from phosphor, hydrogen and fluorine with the target being to evaluate accurately their ionization potentials and electron affinities, as well as influence fluorine on the ionization potential of phosphor as a central atom. To determine the accuracy of hybrid density functional methods for computing those energies, ionization energies for hydrogen, fluorine and phosphor were calculated and compared with the experimental and CBSQ values. To demonstrate the accuracy of this method, both the ionization potential and the electron affinity for phosphorus and fluorine atoms were calculated and compared with the experimental data. For both PF and PF₂, an identical electron affinity of 0.72 eV and for PH and PHF 1.0 eV were suggested.     

Theoretical investigations on analytical potential energy function and spectroscopic parameters for the state b3Πu of dimer 7Li2

The SAC‐CI (symmetry‐adapted‐cluster configuration‐interaction) method presented in Gaussian 03 program package is applied to investigate the adiabatic potential energy curves (PECs) of ⁷Li₂(b³Π_u). These calculations are performed at numbers of basis sets, such as 6‐311++G(3df,3pd), 6‐311++G(2df,2pd), 6‐311++G(df,pd), D95V++, D95(3df,3pd), D95(d,p), cc‐PVTZ, 6‐311++G and 6‐311++G(d,p). All the ab initio calculated points are fitted to the analytic Murrell‐Sorbie functions and then used to compute the spectroscopic parameters. The analytic potential energy function (APEF) for this b³Π_u state is reported. By comparison, the spectroscopic parameters reproduced by the APEF attained at 6‐311++G(2df,2pd) are found to be very close to the latest experimental findings. With the APEF obtained at the SAC‐CI/6‐311++G(2df,2pd) level of theory, a total of 62 vibrational states is found when J = 0. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants for these vibrational states are also reported. The reasonable dissociation limit for this state is deduced using the calculated results at present. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Use of the hydrogen bond potential function in a comparative molecular field analysis (CoMFA) on a set of benzodiazepines

Summary The results of the GRID-Comparative Molecular Field Analysis (CoMFA) were compared with those of the SYBYL-CoMFA in a study of benzodiazepines. The results demonstrate that the hydrogen bonding function using the GRID H₂O probe in a CoMFA can successfully describe the hydrophobic effects of substituents without any bias or preconcept of their effects in the development.     

Surface electronic structure calculations using the MBJLDA potential: Application to Si(111)2 × 1

The Si(111)2 × 1 surface has been widely studied via a range of different experimental and theoretical techniques, and found to adopt a π‐bonded chain configuration. To determine an accurate electronic structure for this system, however, it has been found necessary to use sophisticated and very computationally expensive methods such as GW or hybrid functionals. In this article, we show that the MBJLDA approach, originally proposed by Tran and Blaha for bulk materials (Tran and Blaha, Phys. Rev. Lett. 2009, 102, 226401), yields results which are comparable to GW, and generally superior to those obtained from hybrid functional density functional theory calculations. The MBJLDA method is also substantially more computationally efficient. A procedure and justification for the application of the MBJLDA approach to surfaces in general is also provided. © 2014 Wiley Periodicals, Inc.     

Automated exploration of stable isomers of H(+)(H(2)O)(n) (n = 5-7) via ab initio calculations: An application of the anharmonic downward distortion following algorithm

Isomers of protonated water clusters H(+)(H(2)O)(n) (n = 5-7) have been explored on ab initio potential energy surfaces by means of the anharmonic downward distortion following algorithm. Totally, 9, 24, and 131 isomers for n = 5, 6, and 7, respectively, were located by the automatic exploration, and all of known important isomers previously reported by conventional geometry optimization approaches have been included in the present results. Moreover, structure transitions depending on n and temperature, which were observed by experimental studies, could be reproduced via thermodynamic simulation on the basis of the superposition approach and the present isomer sets.     

Banana-shaped molecules peculiarly oriented in a magnetic field: (2)H NMR spectroscopy and quantum mechanical calculations.

The orientational properties of the banana-shaped liquid crystal 4-chloro-1,3-phenylenebis{4-[4'-(10-undecenyloxy)]benzoyloxy} benzoate (ClPbis11BB) are reported in the nematic phase under the effect of an external magnetic field. A new hypothesis, which states that the central ring of the aromatic core is oriented perpendicularly to the external magnetic field, is proposed. In support of this hypothesis, a series of studies based on (2)H NMR spectroscopy, both in the bulk and in solution, are discussed. (2)H NMR measurements on three selectively deuterium-labelled isotopomers are presented, together with DFT results from B3LYP/cc-pvDz calculations performed on the aromatic core. The rather flat shape of the investigated intramolecular energy surface allows for several different conformations to be populated, the computed magnetic susceptibilities of which are consistent with the proposed hypothesis of peculiar orientation of banana-shaped molecules. Moreover, the orientation of the magnetic susceptibility tensor is shown to be strongly dependent on the internal conformation of the banana-shaped molecules.     

Effective potential energy curves of H2 molecule evolving in a strong time‐dependent magnetic field

Evolution of hydrogen molecule, starting initially from its field‐free ground state, in a time‐dependent (TD) magnetic field of order 10¹¹ G is presented in a parallel internuclear axis and magnetic field‐axis configuration. Effective potential energy curves (EPECs), in terms of exchange and correlation energy, of the hydrogen molecule as a function of TD magnetic‐field strength, are analyzed through TD density functional computations based on a quantum fluid dynamics approach. The numerical computations are performed for internuclear separation R ranging from 0.1 to 14.0 a.u. The EPECs exhibit field‐dependent significant potential‐well minima both at large internuclear separations and at short internuclear separations with a considerable increase in the exchange and correlation energy of the hydrogen molecule. The results, when compared with the time‐independent (TI) studies involving static TI magnetic fields, reveal TD behavior of field‐dependent crossovers between different spin‐states of hydrogen molecule as indicated by the TI investigations in static magnetic fields. Besides this, present work reveals interesting dynamics in the TD total‐electronic charge‐density distribution of the hydrogen molecule. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

On the ion‐pair dissociation mechanisms in the small NaCl·(H2O)6 cluster: A perspective from reaction path search calculations

We performed reaction path search calculations for the NaCl·(H₂O)₆ cluster using the global reaction route mapping (GRRM) code to understand the atomic‐level mechanisms of the NaCl → Na⁺ + Cl⁻ ionic dissociation induced by water solvents. Low‐lying minima, transition states connecting two local minima and corresponding intrinsic reaction coordinates on the potential energy surface are explored. We found that the Na Cl distances at the transitions states for the dissociation pathways were distributed in a relatively wide range of 2.7–3.7 Å and that the Na Cl distance at the transition state did not correlate with the commonly used solvation coordinates. This suggests that the definition of the transition states with specific structures as well as good reaction coordinate is very difficult for the ionic dissociation process even in a small water cluster. © 2018 Wiley Periodicals, Inc.     

HMBC-RELAY: a combined technique for the differentiation of simultaneously detected 2J(C,H) and (n)J(C,H) connectivities

We present a new pulse sequence that detects simultaneously (n)J(C,H) and 2J(C,H) connectivities. The corresponding coherences are created along independent pathways and therefore can be separated into two different subspectra. One spectrum is to show all (n)J(C,H) connectivities and the other is to show exclusively 2J(C,H) connectivities. In contrast to the previously published 2J/(n)J experiment, this sequence detects the 2J(C,H) connectivities via a C,H,H-RELAY pathway leading to an intensification of the 2J(C,H) signals. Strictly, the 2J(C,H) spectrum does not show 2J(C,H) but 3J(H,H) coupling interactions within 13CH(k)-12CH(l) fragments. Therefore, 2J(C,H) signals can appear even if the corresponding 2J(C,H) coupling constant is zero.     

Orientations of the principal components of electric field gradients and internal motions in dihydrogen ligands from the 2H T1 NMR relaxation data in solution

The deuterium spin-lattice relaxation times in (D2) ligands of W, Ru and Os complexes are reviewed and analyzed in terms of the fast internal (D2) motions: free rotation, librations and 180 degrees jumps. The analysis was performed using quadrupolar coupling constant (DQCC) parameters taken from the solid-state 2H NMR spectra and density function theory calculations. It is shown that the calculated DQCC values can be corrected for further use in interpretations of deuterium relaxation times for Ru and Os dihydrogen complexes. The resulting data led to a criterion for using the relaxation data to distinguish fast-spinning dihydrogen ligands. It is shown that the principal components of electric field gradient tensors at D in the dihydrogen ligands are oriented closer to M-D directions.     

Investigation of nu(N-H) and nu(C-N) stretching modes of propylamine (C3H7NH2) in a binary system C3H7NH2 + CH3OH via concentration dependent Raman study and ab initio calculations

Raman spectra of propylamine (C3H7NH2) and its binary mixtures, C3H7NH2 + CH3OH with varying mole fractions of the reference system, C3H7NH2, C were recorded in two widely apart wavenumber regions, 3100-3600 cm(-1) and 1225-1325 cm(-1). In the former region, the two Raman bands at approximately 3305 and approximately 3326 cm(-1), obtained after the line shape analysis, which were assigned to symmetric nu(N-H) and anti-symmetric nu(N-H) stretching modes, respectively, show a downshift upon dilution. However, whereas the nu(N-H) anti-symmetric mode shows a shift of 18.6 cm(-1), the nu(N-H) symmetric mode shows a much smaller shift (5.7 cm(-1)) between neat liquid and high dilution, C = 0.1. This aspect has been explained using the optimized geometries calculated employing ab initio theory (MP2 level) for the neat C3H7NH2 and its different hydrogen-bonded complexes. The linewidth versus concentration plot for the nu(N-H) anti-symmetric stretching mode, however exhibits a distinct maxima at C = 0.4, which has been explained as a slight departure from the concentration fluctuation model. In the latter region, a symmetric peak is observed, which corresponds to nu(C-N) stretching mode, which shows an upshift upon dilution and an almost linear concentration dependence. This has also been explained in terms of the parameters obtained from the optimized geometries of the different hydrogen-bonded complexes.     

Displacive disorder and dielectric relaxation in the stoichiometric bismuth-containing pyrochlores, Bi2MNbO7 (M=In and Sc)

The structural disorder and temperature-dependent dielectric properties of two Bi-based niobate pyrochlore systems which have both previously been reported to occur at the ideal Bi₂(M^IIINb^V)O₇ stoichiometry without any compositional disorder on the pyrochlore A site, namely the Bi₂InNbO₇ (BIN) and Bi₂ScNbO₇ (BSN) pyrochlore systems, have been carefully re-investigated. It is established that A site stoichiometric, Bi-based niobate pyrochlores can indeed exist. Electron diffraction is used to investigate the nature of the displacive disorder therein both at room temperature as well as at close to liquid nitrogen temperature. The characteristic structured diffuse scattering observed arises from β-cristobalite-like, 1-d correlated rotations and associated translations of chains of corner-connected O′Bi₄ tetrahedra. The temperature-dependent dielectric properties including the low temperature dielectric relaxation properties of these A site stoichiometric, Bi-based niobate pyrochlores are also reported as are the micro-Raman spectra thereof. The experimental results suggest that the dipoles as well as the glassy relaxation behaviour in these Bi-based pyrochlores are directly related to these β-cristobalite-like, correlated rotations of 〈110〉 chains of corner-connected O′Bi₄ tetrahedra.     

Theoretical studies of the EPR parameters and local structures for the two Cu2+ centers in Cd(HCOO)2·2H2O

Based on the studies of the electron paramagnetic resonance parameters for two types of the Cu²⁺ centers in Cd(HCOO)₂·2H₂O by using the high‐order perturbation formulas for a 3d⁹ ion in a rhombically elongated octahedron, local structure of the doped copper ion is determined. Research suggests that the impurity Cu²⁺ replaces the host Cd²⁺ and undergoes the local rhombic elongation distortion, characterized by the axial elongation ratios of 4.1%, and 3.8% along the z‐axis and the planar bond length variation ratios of 3.8%, and 3.1% along the x‐axis and y‐axis, for Cu²⁺ Centers, I and II, respectively. The above slightly different axial elongation ratios and planar bond length variation ratios may suitably account for the slightly dissimilar axial g anisotropies Δg (≈0.351 and 0.339) and perpendicular g anisotropies δg (≈0.028 and 0.022) of the two centers, respectively.     

Formation and characterization of an SH(2II32,12) radical beam produced by the F + H2S reaction using a sextupole electric field

An unstable free radical beam of SH was produced by the reaction of fluorine atoms with H₂S and effused from a Teflon nozzle. The beam was focused using sextupole electric fields. Monte Carlo trajectory simulations showed 300 ± 50 K as the rotational temperature for the chemically produced SH, so that an oriented SH beam with (cos θ ) = − 0.28 could be available in the presence of an intense electric field. The beam intensity of the focused SH is estimated to be about 10¹¹ molecule sr⁻¹ s⁻¹.     

Local chain motions of poly(β-hydroxyoctanoate) in the bulk. 13C NMR relaxation study

Variable-temperature ¹³C NMR spin-lattice relaxation times (T₁) and Nuclear Overhauser Enhancements (NOE) at two magnetic fields have been used to study the dynamics of the amorphous part of a semicrystalline sample (33% of crystallinity) of poly(β-hydroxyoctanoate) (PHO). The interpretation of the relaxation data of the backbone carbons was made by employing a number of motional models. Among these, the DLM model offered the best interpretation of the relaxation data in terms of conformational transitions and librational motions of the backbone C? H vectors, and proved to be superior to unimodal distribution functions. The interpretation of temperature- and frequency-dependent T₁ and NOE data of the carbon nuclei in the n-pentyl side chain was made by employing a newly developed composite spectral density function for multiple internal C? C bond rotations of restricted amplitude and chain segmental motion. The temperature dependence of the linewidths of the various protonated carbon resonances of PHO has been discussed in terms of the semicrystalline character of this polymer. © 1995 John Wiley & Sons, Inc.