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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2943-2952 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce the Husimi second moment of momentum (SMM) tensor, which is a function of the position of an electron in a molecule. The major axis of the Husimi SMM tensor evaluated at a point q gives the most probable line of motion for an electron described by a Gaussian wave packet state centered at that point. We investigate two isoelectronic series: N2, NO+, CN−, CO, and HF, H2O, NH3, CH4. For molecules in the multiply bonded series we discover spatial regions in which electron motion is preferentially parallel or perpendicular to the bond axis. We also find a connection between these two regions and the σ and π symmetry contributions to the density. For molecules in the polyatomic series we observe two characteristic local momentum anisotropies. For electrons near a bond axis the preferred motion tends to be transverse to the bond axis, and for electrons near a plane defined by three atoms the preferred motion is normal to the plane. In all systems, the local anisotropy is typically on the order of 1% of the local isotropic component at the same position.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6860-6869 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic position and momentum densities are commonly used to study bonding. The Husimi function, a phase-space density, complements our understanding of these usual densities. Its value at position q and momentum k gives the probability for finding an electron in a Gaussian wave packet state centered at q, k. We have examined these functions for H2, LiH, and N2. We find that the Husimi function provides a useful physical decomposition of coordinate density differences into regions labeled by the momentum and of momentum density or density difference into contributions from different spatial regions.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6399-6408 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Husimi function provides a phase-space view of quantum systems. This paper considers a number of its properties, including ways in which it can be expanded in terms of basis functions. A spectral or "natural'' expansion and an expansion analogous to the Carlson–Keller expansion in terms of coordinate-density momentum-density products are considered, as is a method for separating the angular dependence of the momentum. There is a set of functions in phase space having the same overlap properties as the initial orbital basis in terms of which the charge density matrix is expressed. A Husimi matrix is defined and a scalar product in the space containing such matrices as elements is introduced. The connection with the vector space of density matrices is examined. The Husimi function is related to the Husimi matrix in a way analogous to the relationship between a density matrix and a density, but there is a major difference in that this map can always be inverted. For a harmonic oscillator basis the phase space basis functions, in terms of which the Husimi function is expressed, span a linear space but do not provide a complete set; their products provide a linearly independent set that is complete. It is suggested that similar behavior can be expected for other basis sets.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6283-6287 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A functional of the electron density is defined which has as its value the minimum possible kinetic energy for a system of n electrons having the given density. Analytic expressions are given for upper and lower bounds on the functional, and algorithms by which it can be evaluated are discussed. Use is made of the set of n-respresentable 1-matrices consistent with the given density and a matrix representation in terms of special equidensity orbitals.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 9223-9232 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density matrices for systems with a finite number of states are considered as elements in a vector space. A density matrix that is a convex combination of density matrices that are unitary transformations of some initial density matrix will be closer to, or possibly at the same distance from, the density matrix for the ensemble in which all states are equally occupied, compared with the initial density matrix. This distance is correlated, for few-state systems, with a function simply related to the entropy. This function increases (entropy decreases) with distance from the equal-occupancy density matrix. Other properties of the function are also established. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3651-3661 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A phase space representation is defined for quantum mechanical state functions. General requirements of quantum mechanics and some additional, very reasonable restrictions lead to a representation that is uniquely determined apart from a scaling. With one choice of this scaling, the representation is equivalent to that of Bargmann, although different aspects are emphasized here. Equivalence between position and momentum representations leads to a phase space representation that is invariant to, or at most rescaled by, Fourier transform. Phase space equivalents of some common functions are presented including Cartesian Gaussian basis functions and the hydrogen atom ground state function.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5912-5921 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The matrix of the kinetic energy operator can be divided into two components, one of which is equivalent to the matrix of a function so that it is effectively local. This decomposition is basis-set dependent and is particularly simple when equidensity orbitals are used. It is shown that for a one-dimensional problem the norm of the local component is (square root of)5/3 times the norm of the whole kinetic energy matrix, independent of the density used to define the orbitals. In the three-dimensional case this ratio depends on the density but reasonably simple expressions are obtained. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5898-5911 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have analyzed the locality of matrices of the kinetic energy operator in even-tempered Gaussian and Slater-type (STO) bases, as well as in several three-dimensional, one-dimensional, and pseudo-one-dimensional basis sets of orthogonal polynomials and trigonometric functions. We find that the locality of the kinetic energy matrix in Gaussian bases is dependent upon the basis function parameters, while STO bases are found to always produce kinetic energy matrices which are very nearly equal to the matrices of local operators. In addition, it is observed that in the limit of completeness, the locality measure for all of the one-dimensional basis sets appears to converge to a common value. In the case of a basis set of particle on a ring eigenfunctions, an exact value for this limit has been determined analytically. Three-dimensional and l=0 pseudo-one-dimensional basis sets of orthogonal polynomials give kinetic energy matrices that do not behave similarly in the limit of completeness. It is found that all of these basis sets result in kinetic energy matrices which clearly exhibit nonlocal behavior, except for those involving exponentials. Such bases, like the STO bases, appear always to yield kinetic energy matrices that remain nearly local regardless of the basis function parameters and the number of basis functions used. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 76 (1972), S. 2479-2481 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3320-3323 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The density matrix that leads to a minimum kinetic energy for a given density is considered as a convex superposition of pure states. It is shown that the conditions of stationarity of the kinetic energy and collapse to the given density require that each of the pure state wave functions involved be a single determinant in the same eigenspace of a particular, n-electron Hamiltonian and that all of the orbitals are eigenfunctions of the same effective one-electron Hamiltonian. The potential function arises originally as a Lagrange multiplier associated with the density constraint. In some cases it can (at least in principle) be determined. The role of electron–electron interactions and possible treatment of excited states are considered.
    Type of Medium: Electronic Resource
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