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  • American Institute of Physics  (25)
  • American Institute of Physics (AIP)  (21)
  • Institute of Physics  (10)
  • 1
    Electronic Resource
    Electronic Resource
    Symmetry properties of product states for the system of N n-level atoms (1988)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 29 (1988), S. 1158-1162 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Suppose that the state of a system of N n-level atoms is given by a tensor product of N identical density matrices. The exact formulas are presented that describe the probability that such a system may be found in a pure state with a given symmetry with respect to permutations of atoms. The asymptotic form of these probabilities valid for large N is also derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527958
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  • 2
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    Symmetry properties of product states for the system of N n‐level atoms (1988)
    American Institute of Physics
    Details
    Publication Date: 1988-05-01
    Print ISSN: 0022-2488
    Electronic ISSN: 1089-7658
    Topics: Mathematics , Physics
    Published by American Institute of Physics
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    PAPER CURRENT
  • 3
    Electronic Resource
    Electronic Resource
    Ab initio potential energy surfaces for He–Cl2, Ne–Cl2, and Ar–Cl2 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7745-7755 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The three-dimensional ground state potential energy surfaces for He–Cl2, Ne–Cl2, and Ar–Cl2 have been calculated using the single and double excitation coupled-cluster approach with noniterative perturbational treatment of triple excitations [CCSD(T)]. Calculations have been performed with the augmented correlation consistent triple zeta basis sets supplemented with an additional set of bond functions. Single point calculations for approximate minima have also been performed with several other basis sets including the quadruple zeta basis set (aug-cc-pVQZ) with bond functions. For He–Cl2 and Ar–Cl2 the CCSD(T) results show that the linear configuration is lower in energy than the T-shaped one. For Ne–Cl2 the CCSD(T) approach predicts the T-shaped configuration to be lower in energy. The linear configuration has been found to be more sensitive than the T-shaped one to the changes of the Cl–Cl bond length with the interaction becoming weaker when the Cl–Cl bond length is shortened from its equilibrium value and stronger when it is lengthened. More detailed analysis shows that sensitivity of component energies such as exchange, dispersion, and induction is much greater than that of supermolecule results. The interaction in the T-shaped configuration becomes slightly stronger for shorter Cl–Cl bonds. For He–Cl2 and Ar–Cl2 the larger zero-point vibrational energy of the linear configuration is responsible for making the T-shaped configuration the ground vibrational state. Vibrational effects further increase the difference in energy between the ground state T-shaped configuration of Ne–Cl2 and its linear counterpart. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478683
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  • 4
    Electronic Resource
    Electronic Resource
    Vibrational corrections for some electric and magnetic properties of H2, N2, HF, and CO (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2180-2185 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of vibration on certain electric and magnetic properties of H2, N2, HF, and CO are reported. These properties include electric field gradients, generalized Sternheimer shielding constants, electric-field-gradient polarizabilities, nuclear shielding constants, and shielding polarizabilities. The calculations were based on both electron correlated and uncorrelated methods. Pure vibrational effects, where appropriate, were investigated as well as conventional vibrational averaging. It is found that in many cases vibration plays a very significant role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467724
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  • 5
    Electronic Resource
    Electronic Resource
    Calculations of magnetic properties. IV. Electron-correlated magnetizabilities and rotational g factors for nine small molecules (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2019-2026 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of the magnetizabilities and the rotational g factors at the self-consistent-field (SCF) and second-order Møller–Plesset perturbation theory (MP2) levels of theory are reported for H2, N2, F2, HF, CO, HCN, HNC, H2O, and NH3. The sums rules, that verify the reliability of the calculations, are shown to be well satisfied. The second-order correlation corrections to the magnetizabilities are found to be small, thus substantiating the generally observed good agreement between the experimental and SCF results. Vibrational corrections to the properties of the diatomic molecules are given. Very good agreement is found between the experimental and vibrationally corrected MP2 rotational g factors for the diatomic molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467234
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio study of the He(1S)+CH(X 2Π) interaction (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9525-9535 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces for the 2A′ and 2A″ states of the He(1S)–CH(X 2Π) complex were calculated using supermolecular unrestricted Møller–Plesset perturbation theory and analyzed via the relevant perturbation theory of intermolecular forces. It has been found that the two states are distinctly different. The potential energy surface (PES) of the A″ state has only a single and relatively deep minimum of De≈335 μEh for the T-shaped geometry, at R=5.0 a0 and aitch-theta=100°. The position of this minimum is determined by the exchange repulsion which is substantially reduced at this geometry. The minimum is unusually deep for a complex of He, and it can be viewed as an example of an incipient chemical bond. In contrast, the A′ state's PES represents a typical van der Waals interaction which is characterized by two similarly deep minima. The shape and location of these minima are determined primarily by the anisotropy of the dispersion component. The first minimum occurs for the collinear He–C–H arrangement, at R≈7.5 a0, and aitch-theta=0°, and is 55 μEh deep. The second minimum has a troughlike form which joins the region between R=7.5 a0, aitch-theta=140° and R=8.0 a0, aitch-theta=180°. The lowest point is approximately 54 μEh deep and occurs at R=7.5 a0 and aitch-theta=140°. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472820
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  • 7
    Electronic Resource
    Electronic Resource
    Partitioning of interaction energy in van der Waals complexes involving excited state species: The He(1S)+Cl2(B 3Πu) interaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10116-10127 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The partitioning of interaction energy between a closed-shell and an open-shell system is proposed. This allows us to describe the unrestricted Møller–Plesset interaction energy as a sum of fundamental contributions: electrostatic, exchange, induction and dispersion. The supermolecular energies derived within unrestricted Møller–Plesset perturbation theory are analyzed in terms of perturbation theory of intermolecular forces. The latter has been generalized to allow for the description of monomer wave functions within the unrestricted Hartree–Fock approach. The method is applied to the potential energy surfaces for the first excited triplet states, 3A′ and 3A″, of the He+Cl2(3Πu) complex. The 3A′ and 3A″ potential energy surfaces have different shapes. The lower one, 3A′, has a single minimum for the T-shaped structure. The higher one, 3A″, has the global minimum for the T-shaped structure and the secondary minimum for a linear orientation. The calculated well depth for the 3A′ state is 31.1 cm−1 at the 3.75 A(ring) intersystem separation at the UMP2 level with extended basis set involving bond functions. The 3A″ well depth is approximately 2.3 cm−1 smaller at this level. This order is reversed by higher correlation effects. The angular and radial behaviors of the individual components of the 3A′ and 3A″ interaction energies are compared to reveal the different nature of interaction energies in both states. A comparison with the ground state reveals that the A″ state has a typical van der Waals character similar to that of the ground state. The A′ state, on the other hand, differs considerably from the ground state. The A′ and A″ states differ primarily in different role of the intramonomer correlation effects. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469913
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  • 8
    Electronic Resource
    Electronic Resource
    Convergence properties of coupled Hartree–Fock theory of intermolecular interactions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7545-7554 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction between a helium atom and a proton is analyzed using coupled Hartree–Fock perturbation theory in the polarization approximation. It is shown that even for relatively short interatomic separations the perturbation expansion converges and its sum is identical with the supermolecule interaction energy. Similar behavior is observed for molecule–proton complexes although the convergence may be worse and, as an illustration, calculations for H2O–H+ are presented. A detailed analysis of the electrostatic component of the interaction energy between He and H+ shows the failure of a long range multipole expansion in correcting the secondary basis set superposition error. Polarization approximation perturbation theory is also used to analyze interactions for He–Li+ and He–Na+. The results for interatomic distances of 8.0 and 10.0 a0 for both the basis sets of the monomers, and the basis set of the entire complex are in excellent agreement with the counterpoise-corrected interaction energies, and thus show the need to remove the basis set superposition error.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463474
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of dispersion interaction: Noble gas dimers (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8225-8235 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Several approaches for the evaluation of the dispersion energy are analyzed. The two alternative derivation schemes of the dispersion energy expression use as a starting point either the Casimir–Polder formula or many-body theory. It is argued that only the second approach offers a framework in which the classification of various effects (correlation, response) is unambiguous. The cases for which the two formulations are equivalent are discussed. Calculations, some of which are more accurate than any previously published results, of the nonexpanded dispersion energies for dimers composed of noble gas atoms are reported by five different methods. The examined approaches range from the uncoupled Hartree–Fock treatment to the time-dependent Hartree–Fock (TDHF) method. Comparison with the experimental C6 coefficients indicates that for each dimer a different method offers the best approximation to the "true'' dispersion energy. The nonexpanded TDHF dispersion energies are compared with the expanded ones evaluated by using the procedure of Tang and Toennies. The agreement is fair for He–Ne, Ne2, and Ar2 complexes, but for the He dimer the series representing the dispersion energy is found to diverge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462327
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  • 10
    Electronic Resource
    Electronic Resource
    Hypermagnetizability anisotropy (Cotton–Mouton effect) for H2 and D2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6686-6697 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Explicitly electron-correlated wave functions have been used to calculate the hypermagnetizability anisotropy (Δη) for H2 and D2. This property is the essential feature of the birefringence of a material in the presence of a magnetic field (the Cotton–Mouton effect). The calculations were carried out in the framework of perturbation theory and both dispersion and vibrational effects were fully taken into account. A detailed analysis of our results is made and it is concluded that electron correlation and "pure'' vibrational effects are less important than vibrational averaging and dispersion. The experimental results are only in fair agreement with our theoretical ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460245
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