Open-shell calculation on molecules with icosahedral symmetry

Klimko, G. T.; Mestechkin, M. M.; Whyman, G.E.

doi:10.1007/bf00672880

Cited by 13 publications

(9 citation statements)

References 19 publications

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“…Already the Hfickel estimation shows that the lowest unoccupied molecular orbital (MO) of C6o belongs to the triply degenerate tlu level [1 1]. This point is confirmed by calculation [12] of various properties of C6o, taking into account the interelectron repulsion, which are in good agreement with the subsequent measurements. Thus, the presence of three K atoms for each C6o molecule leads again to a half-filled degenerate band tlu in the K3C6o sample.…”

Section: Introductionsupporting

confidence: 67%

“…The last simple observation which is evident from (12) is that R, is independent of the normalization of the geminal g(rl, r2) as well as tp, in (1) due to (3). In other words all #2 may be multiplied by a common numerical factor c and should be normalized l #2 = 1.…”

Section: The Bcs Model and Macroscopic Limit Of Agpmentioning

confidence: 77%

“…Thus, the presence of three K atoms for each C6o molecule leads again to a half-filled degenerate band tlu in the K3C6o sample. Indeed in the C63o anion within the K3C6o crystal the tlu level remains half-filled: our calculation in [13] using the same approximation as [12] shows that the lowest electronic term of C~o is 4Ag.…”

Section: Introductionmentioning

confidence: 91%

“…,-,-~,-1/q., 217) = (12) t'*i l~j "In -2/Vln 9 From (5) some useful identities follow 9 "2 n(iJ) "" (13) q, = q(i~ l fl2 "k-q~i), q(i)_ 1 = i~,j ~ln_ 2 "~-q(i~ l, etc.…”

Section: The Bcs Model and Macroscopic Limit Of Agpmentioning

confidence: 98%

“…Hence a large occupational number may appear only from the first sum of (11) as an eigenvalue of matrix L~ ). In the case of the ETF where all p~ = 1/l, (11) and (12) are reduced to (7). In particular, the matrix elements LI~ ~ and LI~ ) are independent of i and j here, and the matrix LI~ ) can be explicitly diagonalized [221 to give the macroscopic eigenvalue in (10).…”

Section: The Bcs Model and Macroscopic Limit Of Agpmentioning

confidence: 99%

See 4 more Smart Citations

Molecular viewpoint on high-temperature superconductivity Importance of orbital degeneracy

Mestechkin¹,

Whyman²,

Klimko³

1994

Molecular Physics

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It is shown that the antisymmetrized geminal power wavefunction (AGP) in the macroscopic limit and the Bardeen-Cooper-Schrieffer (BCS) superconductivity model with fixed mean number of electrons coincide to arbitrary order in deviations from the extreme-type function which is considered as the carrier of the superconductivity property. Variational equations for the AGP in the macroscopic limit are formulated in terms of two sets of parameters, E i and Ai, which under simplifying assumptions reduce to eigenvalues of the open-shell Roothaan one-electron Hamiltonian and to the BCS energy gap parameter, respectively. The superconducting state is shown to be stable for the solution of these equations with a macroscopic number of non-zero Ai and of degenerate E i = E z at the Fermi level E v. The macroscopic contribution to the maximal pair occupation number which is responsible for the superconductivity is expressed as a mean value of A~/[(e i -ev) 2 + A~]. The formulated non-zero temperature version of the equations for e~, A~ is able to describe the superconducting phase transition. On this ground the necessary condition of stabilization of the superconducting state is formulated that is the existence of the macroscopic-fold near-degenerate and almost half-filled level. As is shown it is realized in the energy band structure of doped fullerides, copper oxide ceramics and perovskite-type crystals, e.g. BaBiO 3. The additional requirement of negativity of exchange interelectron-interaction integrals may be satisfied not only by the known vibronic mechanism but also, as is demonstrated, by the polarization potential of an environment in a plane layer of stratum structures.

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Section: Introductionsupporting

confidence: 67%

Section: The Bcs Model and Macroscopic Limit Of Agpmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 91%

“…,-,-~,-1/q., 217) = (12) t'*i l~j "In -2/Vln 9 From (5) some useful identities follow 9 "2 n(iJ) "" (13) q, = q(i~ l fl2 "k-q~i), q(i)_ 1 = i~,j ~ln_ 2 "~-q(i~ l, etc.…”

Section: The Bcs Model and Macroscopic Limit Of Agpmentioning

confidence: 98%