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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio model potential study of local distortions around Cr+ and Cr3+ defects in fluorite (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8158-8164 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present the results of a theoretical study of the local geometry distortions produced by Cr+ and Cr3+ ions in fluorite, by means of the ab initio environment model potential method [J. Chem. Phys. 89, 5739 (1988)]. The valence energy and wave function of the (CrF8)q−(q=7,5) clusters embedded in the CaF2 lattice represented by 118 ab initio model potential ions plus 750 point-charge ions are calculated using a short CI, which includes all states related to the dn ionic configuration. A geometry optimization is performed for CaF2@B:(CrF8)7− within the cubic point symmetry and for CaF2@B:(CrF8)5− within the D3d point symmetry; the conclusions of analyses of the multimode Jahn–Teller coupling T1⊗(ε+τ2+τ'2) are used to address the geometry optimization, which is completed by a final unrestricted search. In an attempt to study all the structures proposed along previous experimental studies, the D3d structure corresponding to an octahedral cluster plus two axially displaced fluorines (octahedron+2) is investigated. Taking the ground state energy of the perfect cube as a reference, the results show that the most stable D3d distortion corresponds to an elongated cube in a 4A2g ground state, with an energy of about −1700 cm−1, while the compressed cube and the octahedron+2 structure energies are found to be −780 and +40 000 cm−1, respectively. A joint analysis of the available experimental data and the results of our calculations are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460098
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3762-3773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state equilibrium geometry of alkaline earth dihalides MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I) has been optimized at the Hartree–Fock (HF) level using the Cowan–Griffin relativistic ab initio model potential method and a uniformly good, extended, spd valence basis set. The results show that, according to the method, all magnesium dihalides and CaCl2, CaBr2, and CaI2 are linear, SrF2 and all barium dihalides are bent, and CaF2 and SrCl2, SrBr2, and SrI2 are quasilinear molecules. The alkaline earth (n−1)d orbitals are shown to be responsible for the bending of the heavier molecules while their (n−1)p orbitals contribute considerably to the final quantitative prediction of the apex angle and the relative stability of the bent structures. Relativistic effects are shown to be very small on the bond distances and vibrational frequencies; they are important on the size of the bending barrier of the bent molecules. The results obtained are compared to previous theoretical studies and provide some insight in the interpretation of the contradictory experimental conclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459748
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  • 3
    Electronic Resource
    Electronic Resource
    The ab initio model potential method. First series transition metal elements (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7011-7017 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the ab initio core model potential method the Coulomb and exchange core operators are represented accurately and the valence basis set is the only component of the method which is optimized (following the variational principle) in an atomic valence restricted Hartree–Fock (RHF) calculation. In this paper we present the nonrelativistic Ar-like and Mg-like core model potentials and valence Gaussian basis sets for the first series transition metal elements. The pilot RHF molecular calculations on ScO, MnO, CuO, and ScS show that freezing the 3s orbital is safe all along the transition series but the same is true for the 3p orbital only towards the end of the series. A good agreement exists between the all-electron and model potential results if the same type of valence part of the basis set is used: 0.01 A(ring) in Re and 25 cm−1 in ν¯e.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457317
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  • 4
    Electronic Resource
    Electronic Resource
    The ab initio model potential representation of the crystalline environment. Theoretical study of the local distortion on NaCl:Cu+ (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5739-5746 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we formulate a model potential approach to take into account the crystalline environment within the Hartree–Fock–Roothaan formalism. The formulation is based on the assumption that the theory of separability of many-electron systems may be applicable to the group of electrons within a reference cluster and the groups of electrons on a set of external lattice sites which, in turn, can be represented according to the ab initio model potential method. The characteristics of the model potentials permit to analyze the contributions to the cluster energies and wave functions of different environmental effects, such as point-charge and charge-density Coulomb interactions and quantum interactions (exchange and orthogonality). The formalism is applied to the SCF calculation on the ground state of the octahedaral CuCl5−6 cluster (all-electron calculation) embedded in a NaCl lattice which is represented by 118 model-potential ions and 604 point-charge ions. The calculation reveals that (i) the quantum interactions between the CuCl5−6 cluster and the rest of the lattice play an important role in determining the Cu–Cl distance and (ii) a considerable local distortion around the Cu+ impurity is predicted in which the Cl− ions move towards the Cu+ impurity about 0.1 A(ring). These results are in qualitative agreement with recent EXAFS studies; however, the predicted distortion is smaller than the one suggested by the EXAFS measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455549
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  • 5
    Electronic Resource
    Electronic Resource
    The ab initio model potential method. Second series transition metal elements (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5843-5850 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ab initio core method potential model (AIMP) has already been presented in its nonrelativistic version and applied to the main group and first series transition metal elements [J. Chem. Phys. 86, 2132 (1987); 91, 7011 (1989)]. In this paper we extend the AIMP method to include relativistic effects within the Cowan–Griffin approximation and we present relativistic Zn-like core model potentials and valence basis sets, as well as their nonrelativistic Zn-like core and Kr-like core counterparts. The pilot molecular calculations on YO, TcO, AgO, and AgH reveal that the 4p orbital is indeed a core orbital only at the end part of the series, whereas the 4s orbital can be safely frozen from Y to Cd. The all-electron and model potential results agree in 0.01–0.02 A(ring) in Re and 25–50 cm−1 in ν¯e if the same type of valence part of the basis set is used. The comparison of the relativistic results on AgH with those of the all-electron Dirac–Fock calculations by Lee and McLean is satisfactory: the absolute value of Re is reproduced within the 0.01 A(ring) margin and the relativistic contraction of 0.077 A(ring) is also very well reproduced (0.075 A(ring)). Finally, the relative magnitude of the effects of the core orbital change, mass–velocity potential, and Darwin potential on the net relativistic effects are analyzed in the four molecules studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459580
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  • 6
    Electronic Resource
    Electronic Resource
    The ab initio model potential method. Main group elements (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2132-2145 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present the ab initio core model potential method, in which the Coulomb and exchange core operators Jc and Kc are represented as accurately as possible using adequate local and nonlocal potentials, and the valence basis set is optimized in atomic MP SCF calculations following the variational principle. Nonrelativistic model potential parameters and valence basis sets are presented for the main group elements from Li to Xe. The pilot SCF molecular calculations on the ground states of N2, P2, As2, Sb2, and CaO show a good agreement between all-electron and model potential results, in particular the changes observed in molecular results due to improvements of the valence part of the all-electron basis set are reproduced by the model potential calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452111
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  • 7
    Electronic Resource
    Electronic Resource
    Structure and spectroscopy of Pa4+ defects in Cs2ZrCl6. An ab initio theoretical study (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5554-5560 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present the results of spin–orbit relativistic ab initio model potential embedded cluster calculations on (PaCl6)2− embedded in a reliable representation of the Cs2ZrCl6 host. Totally symmetric local distortions and vibrational frequencies are calculated for all the states of the 5f1 and 6d1 manifolds, as well as the corresponding 5f↔6d transition energies and the shape of the 5f(Γ8u)←6d(Γ8g) fluorescence band. An excellent overall agreement with available experimental data is observed which allows us to conclude that the quality of the spin–orbit operators used is very high for actinide elements, as was already known for transition metal and lanthanide elements. Furthermore, it is concluded that the structural and spectroscopic information produced here is very reliable and that the 6d(Γ8g′) state is around 10 000 cm−1 higher in energy than it was thought; our calculations suggest a value of 30 000 cm−1 for the 10Dq parameter of Pa4+ in Cs2ZrCl6, which would be compatible with the lower limit of 20 000 cm−1 accepted for Ce3+ in Cs2NaYCl6. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398092
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  • 8
    Electronic Resource
    Electronic Resource
    Alternative configuration interaction expansions for transition metal ions with intermediate oxidation states in crystals: The structure and absorption spectrum of Cs2GeF6:Mn4+ (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7061-7065 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vertical absorption spectrum of the MnF62− cluster embedded in the Cs2GeF6 host crystal was recently calculated using the averaged coupled pair functional method leading to very large discrepancies with accurate one- and two-photon spectra. The same multiconfigurational expansions had previously been successful in similar systems which involved transition metal impurities in lower oxidation states. In this paper we show that the ligand-to-metal charge transfer configurations become so important in this intermediate oxidation state impurity (and, possibly, non-negligible ligand–ligand weak bonding interactions) that none of the 18 molecular orbitals of F 2p character should be left inactive in the correlation treatment. This requirement can be satisfied in MnF62− because of the higher oxidation state of manganese, which enhances the ligand field splittings in the Mn 3d3 configuration manifold so much that one dominant Mn 3d3 configuration rather than the full Mn 3d3 active space can be used as a single reference for single and double excitations from all occupied ligand 2p orbitals. The results of this work, together with those of previous studies, outline two different alternative truncation schemes of the valence electron correlation which produce the same, necessary, high accuracy in structural and spectroscopic properties of transition metal ions doped in ionic crystals. Whether one or the other should be used depends, basically, on the formal oxidation state of the transition metal impurity. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1404140
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  • 9
    Electronic Resource
    Electronic Resource
    The ab initio model potential method: Lanthanide and actinide elements (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 118-129 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present relativistic core ab initio model potentials based on atomic Cowan–Griffin calculations, together with Wood–Boring spin-orbit operators and optimized Gaussian valence basis sets, for the lanthanide elements Ce to Lu and for the actinide elements Th to Lr. This completes the chemically relevant part of the Periodic Table. A [Kr,4d] core was chosen for Ce–Lu and a [Xe,4f,5d] core was chosen for Th–Lr. Minimal (14s10p9d8f )/[2s1p1d1f] and (14s10p11d9f )/[2s1p1d1f] valence basis sets were, respectively, optimized for Ce–Lu and Th–Lr, and a [6s5p5d4f] contraction is recommended for all these 28 elements in molecular calculations. The atomic and molecular results show the same good quality already observed for the main-group elements and the transition metal elements. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1330209
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  • 10
    Electronic Resource
    Electronic Resource
    Quasirelativistic ab initio model potential calculations on the group IV hydrides (XH2, XH4; X=Si,Ge,Sn,Pb) and oxides (XO; X=Ge,Sn,Pb) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4049-4054 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present the results of a systematic comparison between the values of the bond lengths, bond angles, and vibrational frequencies of group IV dihydrides and tetrahydrides (XH2, XH4, X=Si,Ge,Sn,Pb), and monoxides (XO, X=Ge,Sn,Pb), as well as the XH4→XH2+H2 reaction energies, calculated with the spin-free (Cowan–Griffin based) quasirelativistic ab initio core model potential method (AIMP) and the all-electron Dirac–Hartree–Fock method (DHF), using basis sets of similar quality in their valence part. The deviations between the AIMP and DHF results on the absolute values of the properties and on the sizes of the relativistic effects are of the order expected for an effective core potential method and follow the expected tendency of importance of the spin–orbit effects. The quality of the AIMP results is shown to be consistent going down the group IV of the Periodic Table.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467522
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