Ni2 分子的自旋极化效应

The density functional（B3P86）method has been used to optimize the structure of Ni2 molecule. Results show that the ground state for Ni2 molecule is 5 multiple state,not 1 multiple state and 3 multiple state the literatures concluded. That shows the spin polarization effect of Ni2 molecule of transition metal elements for the first time. They take 1 multiple state and 3 multiple state as the ground state of the Ni2 molecule because the minimal energy value of 1 multiple state,3 multiple state and 5 multiple state of Ni2 molecule are very close to each other. Meanwhile,we have not found out any spin pollution and the ground state wave function doesn't mingle with wave function with higher energy state. The result shows that the ground state for Ni2 molecule is 5 multiple state,which shows the spin polarization effect of Ni2 molecule of transition metal elements. That is,there exist 4 parallel spin electrons,at this time;the number of the non-conjugated electron is the most. These electrons occupy different spacious tracks so that the energy of Ni2 molecule reduces to the minimum. It shows that the effect of parallel spin of Ni2 molecule is larger than the effect of the conjugated molecule. It is obviously related to the effect of electron d delocalization. The Murrell-Sorbie potential function with the parameters for ground state for Ni2 molecule are also derived. Dissociation energy of the ground state Ni2 molecule is 1.835 eV,the equilibrium bond length is 0.2243 nm,and the vibration frequency is 262. 35 cm-1 . The force constants f2,f3 and f4 are 1.1901 aJ / nm2,-5.8723 aJ/nm3,21.2505 aJ/nm4 respectively.     

Electron correlation in the GK state of the hydrogen molecule

The second excited (1)Sigma(g)(+) state of the hydrogen molecule, the so-called GK state, has a potential energy curve with double minima. At the united atom limit it converges to the 1s3d configuration of He. At large internuclear distances R, it dissociates to two separated atoms, one in the ground state and another in the 2p excited state. Radial pair density calculations and natural orbital analyses reveal unusual effect of electron correlation around the K minimum of the potential energy curve. As R>2.0 a.u., a natural orbital of sigma(u) symmetry joins the two natural orbitals of sigma(g) symmetry at smaller R. The average interelectronic distance decreases as the internuclear distance increases from R=2.0 to 3.0 a.u. Around R=3.0 a.u. the singly peaked pair density curve splits into two peaks. The inner peak can be attributed to the formation of the ionic electron configuration (1s)(2), where both 1s electrons are on the same nucleus. As the two 1s electrons run into different nuclei, one of the two 1s electrons is promoted to the 2p state, which results in the outer peak in the pair density curve. The Rydberg 1s2p configuration persists as the nuclei stretch, and becomes dominant at large R where four natural orbitals, two of sigma(g) and two of sigma(u) symmetry, become responsible.     

The effect of electronic correlation on molecular wavefunctions

The minimal basis set Hartree-Fock and full-CI wavefunctions of some molecules (N₂, CO, BH₂, CH₄) are analyzed in terms of their valence-bond components. The internal valence correlation has dramatic effects on this distribution. The coefficients of the ionic forms decrease very rapidly with ionicity; the largest coefficients concern neutral determinants with maximum spreading of the p electrons which are multiplied by important factors (3 to 10) by the CI. The neutral components with two electrons is the same p AO are increased to a lesser extent. Correlation decreases the charge fluctuation in a dramatic way. On the other hand the atomic spin fluctuation increases under correlation. When the main atomic configuration is not the ground state one (as in BH₂ or CH₄) the correlation does not increase the components of the atomic ground states, and has little effect on hybridization. These various trends reflect a compromise between the necessity of bond building between electrons of opposite spins and the tendency of the atoms to increase their components in their low energy configurations.     

Accounting for correlations with core electrons by means of the generalized relativistic effective core potentials: atoms Hg and Pb and their compounds

A way to account for correlations between the chemically active (valence) and innermore (core) electrons in the framework of the generalized relativistic effective core potential (GRECP) method is suggested. The "correlated" GRECP's (CGRECP's) are generated for the Hg and Pb atoms. Only correlations for the external 12 and 4 electrons of them, correspondingly, should be treated explicitly in the subsequent calculations with these CGRECP's whereas the innermore electrons are excluded from the calculations. Results of atomic calculations with the correlated and earlier GRECP versions are compared with the corresponding all-electron Dirac-Coulomb values. Calculations with the above GRECP's and CGRECP's are also carried out for the lowest-lying states of the HgH molecule and its cation and for the ground state of the PbO molecule, as compared to earlier calculations and experimental data. The accuracy for the vibrational frequencies is increased up to an order of magnitude and the errors for the bond lengths (rotational constants) are decreased in about two times when the correlated GRECP's are applied instead of earlier GRECP versions employing the same innercore-outercore-valence partitioning.     

Generation and detection of entanglement in coincident photo-Auger electron spectroscopy of linear rotating molecules

We have derived a simple analytical expression which completely characterizes entanglement properties of the spin state of a photo-Auger electron pair. These two electrons are sequentially emitted from a rotating linear molecule in the absence of any spin-dependent interactions. This expression comes out to be identical to that already obtained [Chandra and Ghosh, Phys. Rev. A 70 (2004) 060306(R)] for similar studies in atomic targets without spin–orbit interaction. Thus, inner-shell ionization of both atoms and of linear molecules becomes a readily available universal factory for producing bipartite entangled states of electrons.     

The absorption coefficient of a polar liquid with solvated electrons

An equation for the absorption coefficient of a polar liquid with excess (solvated) electrons is derived. It is taken into account that (1) each excess electron can for a certain time reside on only one liquid molecule (during this time, the molecule is in the anion-resonance state), and (2) a polar liquid is electrostatically nonuniform because it has different local potentials, which can be calculated for each molecule. The probabilities of quantum movements of excess electrons in a liquid from one molecule to another caused by the absorption of photons are considered.     

Angular correlation of electrons in the ground state of helium

The spatial angular correlation of electrons in the ground state of the helium atom has been examined using configuration interaction and Hylleraas wave-functions. It was found that, in general, the average angle between the electrons is not a maximum when the two electrons are at the same distance from the nucleus. For configuration interaction wave-functions there is a position of the electrons for which the average value of the angle between the electrons is a maximum. Hylleraas wave-functions do not show this behavior.     

Fukui function as correlation hole

The Fukui Function concept of the theory of chemical reactivity is identified as the negative asymptotic exchange-correlation hole, when one electrons wanders far away from the rest of the molecule. The appropriate two-electron measures of the electron density responses for an electrophilic, nucleophilic, and radical attacks are proposed, and the exact correspondence with the electron density of the Frontier Orbitals is established for the hypothetical Kohn–Sham system.     

Simplistic classical probabilistic model of superexcited states of molecules

The decay processes in the superexcited state of a molecule are investigated theoretically in terms of a classical trajectory method. The simplest model of a diatomic molecule is considered. Particular attention is payed to the branching ratio for preionization and predissociation, and to the energy distribution of the ejected electrons. New formulas of practical use are derived for these two quantities.     

Local and long-range correlation in extended systems

In this paper ab initio electron correlation studies are described for small (formaldehyde with 16 electrons), intermediate (1-oxy-3-aza-butadiene, 30 electrons) and large (cytosine, 58 electrons) covalent molecules using localized perturbation theory up to the third order and including some fourth-order localization correction terms as well. Long-range and local correlation effects are separated in a mathematically well-defined manner and the effect of various atomic basis sets is investigated. For comparison CI (singles and doubles) calculations were also carried out for formaldehyde.     

SCF and CI Studies of Hund's rules for the effects of electronic correlation and delocalization. I

In connection with the reinterpretation of Hund's multiplicity rules for molecules, a detailed study has been made of the energy differences in the total energy and its components for the triplet and singlet Π_u states of the hydrogen molecule and the analogous states of the four- and six-membered hydrogen atom rings. For the hydrogen molecule, both SCF and CI studies indicated that the outer electron is considerably more contracted in the triplet than in the singlet state. In both approximations, the energy difference is dominated for all bond distances of chemical and physical significance by the electron-nuclear attraction component and not by the electron repulsion component as predicted by simple first-order perturbation theory. Although the correlation energy for each of the states is of the same magnitude as the energy differences considered here, the difference of the correlation energies is much smaller. It had little effect on the qualitative differences between these states of the hydrogen molecule. For the four- and six-membered rings, SCF studies were made on the lowest singlet and triplet states where one electron was promoted from the σ_g to a Π_u orbital. Even though the coupled electrons were more delocalized in these cases, the electron repulsion became relatively more important. However in all cases, the lower state had the highest electron repulsion energy and lower electron-nuclear attraction. The triplet state continued to have the more contracted outer open-shell orbital.     

Spectral investigations on 1,5-dipiperidino anthraquinone

Optical absorption, fluorescence emission and surface enhanced Raman spectra of 1,5-dipiperidino anthraquinone (1,5-DPAQ) have been examined to elucidate the nature of molecule in different environments. Fluorescence emission and optical absorption measurements show that the polarity of the solvent plays a vital role through intermolecular hydrogen bonding and reorientational motion of solvent molecule around excited state fluorophore. Anisotropy measurement gives the angle between absorption and emission transition dipoles. The vibrational features observed in surface enhanced Raman spectroscopy (SERS) suggest that the molecules are chemisorbed. The adsorption of the molecule is through pi electrons in the anthraquinone ring and the axial lone pair of electrons of nitrogen. The orientation of the molecule is found to be 'flat-on'.     

Electron correlation and bond-length alternation in polyene chains

The PPP model is used to consider polyene chains in the ground state with allowance for the interaction of the electrons with core deformations. The stationary wave functions describing the electron correlations are derived as antisymmetrized products of two-electron functions optimized with respect to all variational parameters. The bond-length alternation can be related to the characteristics of the electron-electron potential; one can allow approximately for the effects of interaction between electrons at adjacent centers on the alternation by renormalizing the parameters in the Hubbard model.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 263–270, May–June, 1986.In am indebted to I. I. Ukrainskii for a discussion of this.     

Visualizing molecular wavefunctions using Monte Carlo methods

Using explicitly correlated wavefunctions and variational Monte Carlo we calculate the electron density, the electron density difference, the intracule density, the extracule density, two forms of the kinetic energy density, the Laplacian of the electron density, the Laplacian of the intracule density, and the Laplacian of the extracule density on a dense grid of points for the ground state of the hydrogen molecule at three internuclear distances (0.6, 1.4, 8.0). With these values we construct a contour plot of each function and describe how it can be used to visualize the distribution of electrons in this molecule. We also examine the influence of electron correlation on each expectation value by calculating each function with a Hartree–Fock wavefunction and then comparing these values with our explicitly correlated values. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Dibenzo[a,c]phenazine: a polarity-insensitive hydrogen-bonding probe

A derivative of phenazine, dibenzo[a,c]phenazine (DBPZ), can be used as a very good hydrogen-bonding probe unlike its parent phenazine molecule. Steady-state absorption and fluorescence studies reveal that DBPZ is completely insensitive to polarity of the medium. However, DBPZ can form a hydrogen bond very efficiently in its first excited singlet state. The extent of this excited-state hydrogen-bond formation depends both on size and on hydrogen-bond donor ability of the solvents. Time-resolved fluorescence studies and theoretical calculations also suggest that this hydrogen-bond formation is much more favorable in the excited state as compared to the ground state. In the excited state, the electron density is pushed toward the nitrogen atoms from the benzene rings, thereby increasing the dipole moment of the DBPZ molecule. Although the dipole moment of DBPZ increases upon photoexcitation, like other polarity probes, the molecule remains fully insensitive to the polarity of the interacting solvent. This unusual behavior of DBPZ as compared to simple phenazine and other polarity probes is due to the structure of the molecule. Hydrogen atoms at the 1 and 8 positions of DBPZ are sterically interacting with a lone pair of electrons on the proximate nitrogen atoms and make both of the nitrogen atoms inaccessible to solvent molecules. For this reason, DBPZ cannot sense the polarity of the medium. However, DBPZ can only sense solvents, those that have hydrogen with some electropositive nature, that is, the hydrogen-bond donating solvents. Hydrogen being the smallest among all elements can only interact with the lone pair of electrons of nitrogen atoms. Thus, DBPZ can act as a sensor for the hydrogen-bond donating solvents irrespective of their dielectrics.     

On the effect of 4f electrons on the structural characteristics of lanthanide trihalides: computational and electron diffraction study of dysprosium trichloride

The molecular and electronic structure of dysprosium trichloride, DyCl(3), was calculated by high-level quantum chemical methods in order to learn about the effect of the partially filled 4f subshell and of the possible spin-orbit coupling on them. High-temperature electron diffraction studies of DyCl(3) were also carried out so that we could compare the computed geometry with the experimental one, after thermal corrections on the latter. Dysprosium monochloride, DyCl, and the dimer of dysprosium trichloride, Dy(2)Cl(6), were also investigated by computation. We found that the electron configuration of the 4f subshell does not influence the geometry of the trichloride monomer molecule as the ground state and first excited state molecules have the same geometry. Nonetheless, taking the 4f electrons into account in the calculation, together with the 5s and 5p electrons, is important in order to get geometrical parameters consistent with the results from experiment. Based on electron diffraction and different levels of computation, the suggested equilibrium bond length (r(e)) of DyCl(3) is 2.443(14) A, while the thermal average distance (r(g)) from electron diffraction is 2.459(11) A. The molecule is trigonal planar in equilibrium. Although the ground electronic state splits due to spin-orbit coupling, the lowering of the total electronic energy is very small (about 0.025 hartree) and the geometrical parameters are not affected. In contrast with the monomeric trichloride molecule, the bond angles of the dimer seem to be different for different electronic states, indicating the influence of the 4f electronic configuration on their structure. We carried out an anharmonic analysis of the out-of-plane vibration of the trichloride monomer and found that the vibration is considerably anharmonic at 39.5 cm(-1), compared with the 30.5 cm(-1) harmonic value.     

A theory of elementary photophysical processes with the participation of excess electrons in polar liquids

The main concepts of the new theory of processes with the participation of excess electrons in polar liquids are considered. The theory takes into account that (1) polar liquids are electrostatically inhomogeneous (local potentials on molecules are different) and (2) a molecule can accept an electron for a short time to produce an anion in an unstable state with a certain energy and lifetime. A discrete model of a substance consisting of molecules with constant dipole moments is used. Excess electrons in a liquid are described by energy distribution density, and the behavior of electrons, by quantum mechanics equations. The experimental data on the photoionization of water and aqueous solutions of salts and the low threshold energy of photons (～6.5 eV) at which solvated electrons appear in water are explained. The absorption spectra of water with excess electrons at the first and subsequent time moments after their photogeneration are reproduced theoretically. The dependence of the photoemission of solvated electrons from potassium-ammonia solutions on the energy of photons is interpreted. The continuous spectrum of spontaneous radiation of solvated electrons in liquid ammonia and water is calculated. The optical absorption spectra of solvated electrons in such polar liquids as water and ammonia are reproduced.     

Study of the electronic structure of molecules. XV. Comments on the molecular orbital valency state and on the molecular orbital energies

The valency state (vs) concept is analyzed in the Hartree–Fock approximation. A valency state “standard” is defined for atoms at infinite separation. A molecular orbital valency state (Movs) is defined from a partitioning technique (bond energy analysis) previously introduced for the Hartree–Fock molecular wave functions. The Movs for a given atom in a molecule is much higher in energy than the vs and its energy varies from molecule to molecule depending on the exact field of the surrounding atoms. The examples selected in the discussion are the CH₄ CH₃F, CH₂F₂, CHF₃ and CF₄ molecules. An analysis of the orbital energies is then given in terms of the bond energy. The importance of the rearrangement effects following ionization of inner shell electrons (simulation of ESCA type experiments) is illustrated with computations of the positive ion for methane and its fluoroderivatives. It is concluded that rearrangement following ionization from inner shells is as important as rearrangements following ionization from valency electrons. A direct consequence is that the orbital energies should not be equated to the inner shell ionization potentials. The computation of such ionization potentials agrees to about 99.5% with ESCA data, when the energy of both the neutral and ionic species are computed; the use of the orbital energies limits this agreement to about 95%.     

Real space Hartree-Fock configuration interaction method for complex lateral quantum dot molecules

We present unrestricted Hartree-Fock method coupled with configuration interaction (CI) method (URHF-CI) suitable for the calculation of ground and excited states of large number of electrons localized by complex gate potentials in quasi-two-dimensional quantum dot molecules. The method employs real space finite difference method, incorporating strong magnetic field, for calculating single particle states. The Hartree-Fock method is employed for the calculation of direct and exchange interaction contributions to the ground state energy. The effects of correlations are included in energies and directly in the many-particle wave functions via CI method using a limited set of excitations above the Fermi level. The URHF-CI method and its performance are illustrated on the example of ten electrons confined in a two-dimensional quantum dot molecule.     

Switching individual molecules by light and electrons: From isomerisation to chirality flip

Molecular electronics offers a promising way for constructing nano-electronic devices in future with faster performance and smaller dimensions. For this aim, electronic switches are essential as basic components for storage and logical operations. The main requirements for a molecular switch are reversibility and bistability. This necessitates the existence of at least two different thermally stable forms of a molecule that may be changed repeatedly from one state to the other one through an external stimulus. The transition should then be connected to a measurable change in molecular properties. The development of such molecular switches on the single molecule level is a major challenge on the path towards incorporating molecules as building units into nanoelectronic circuits. Since isomers may differ significantly in physical and chemical properties, isomerisation opens a way for a molecular switch.In this article, an overview is provided over those isomerisation reactions of single molecules adsorbed on surfaces that are investigated with a scanning tunnelling microscope and that have a potential as a molecular switch in future molecular electronics. These are mainly, but not exclusively, constitutional, configurational, and geometric isomerisation reactions. The external stimulus is either light or the possible interaction with the tip of a scanning tunnelling microscope, i.e. electrons, electric field, or mechanical force. Some reactions are similar to those observed for the molecule in the liquid phase, but some are observed or even possible only on a surface. The detailed investigation of the isomerisation yield dependence on several parameters gives insight into the underlying processes of the reaction.