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1
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0012064449
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Examples of the construction of microscopic structures from small numbers of atoms using the scanning tunneling microscope include
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(1991)
Nature
, vol.344
, pp. 524
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Eigler, D.M.1
Schweizer, E.I.2
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30
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84928001957
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If the size of the constriction is large compared with the mean free path of the electrons, then it is known as the Maxwell resistance;
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31
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0001665670
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in the opposite limit, which is the one of interest to us here, it is known as the Sharvin resistance. For a study of the way in which the classical Sharvin result is modified by a quantum-mechanical treatment, see
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(1994)
Phys. Rev. B
, vol.49
, pp. 16581
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Torres, J.A.1
Pascual, J.I.2
Sáenz, J.J.3
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33
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0001344261
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and G.
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(1988)
J. Phys. C
, vol.21
, pp. L209
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Wharam, D.A.1
Thornton, T.J.2
Newbury, R.3
Pepper, M.4
Ahmed, H.5
Frost, J.E.F.6
Hasko, D.G.7
Peacock, D.C.8
Ritchie, D.A.9
Jones, A.C.10
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43
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0001248241
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(1994)
Phys. Rev. Lett.
, vol.72
, pp. 2251
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Olesen, L.1
Lægsgaard, E.2
Stensgaard, I.3
Besenbacher, F.4
Schiøtz, J.5
Stoltze, P.6
Jacobsen, K.W.7
Nørskov, J.K.8
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45
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84928001956
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U. Landman and W. D. Luedtke, in Scanning Tunneling Microscopy III, edited by R. Wiesendanger and H.-J. Güntherodt (Springer, Berlin, 1993), p. 207;
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49
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84928001955
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Cf. also C. Joachim, X. Bouju, and C. Girard, in Atomic and Nanometer-Scale Modification of Materials: Fundamentals and Applications, edited by P. Avouris (Kluwer, Dordrecht, 1993), p. 247 (extended Hückel calculation).
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56
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84928001954
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R. W. Hockney and J. W. Eastwood, Computer Simulation Using Particles (McGraw-Hill, New York, 1981), see p. 212.
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65
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84928001953
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A cubic box with a side length of 22 bohrs was used in the calculations for Al chains described in Sec. IV, but for those cases in which the chains included a S atom, the box was made rectangular, with length 22 bohrs in the z direction as before but 12 bohrs in the x and y directions. This permitted decreasing the N value for the x and y directions with no reduction in accuracy, allowing in turn an increase in N for the z direction and still leaving a net decrease in computer time and storage.
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67
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84928001952
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Another solution to the problem encountered here is to do the whole calculation in the Laue representation;
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70
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84928001951
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We take the electrodes to have rs=2 bohrs, typical of a high-electron-density metal. This parameter is defined by case 4 over 3 π rs3ieq n-1, where n is the mean interior electron number density in the electrodes.
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71
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24444436292
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We take the Al-surface bond length (measured from the Al nucleus to the positive-background edge of the electrode) to be fixed at 2.6 bohrs, which is the calculated bond distance for the case in which nothing else is bonded to the atom [see, ]. We take the Al-Al bond length to be 5.4 bohrs, which is the bond distance calculated for bulk Al using the local-density approximation by V. L. Moruzzi, J. F. Janak, and A. R. Williams, Calculated Electronic Properties of Metals (Pergamon, New York, 1978). We do not try to calculate the bond lengths here because our results are not very sensitive to the exact values of these lengths: for example, expanding all bond lengths in the three-atom Al wire by 0.2 bohr changes the calculated resistance by less than 1%.
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(1994)
Phys. Rev. B
, vol.49
, pp. 2067
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Lang, N.D.1
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73
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84928001950
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In the study of Kalmeyer and Laughlin (Ref. 30), in which the coupling between each of the semi-infinite constant-potential regions (i.e., the electrodes) and the well embedded in the barrier between them is assumed to be small, the conductance at the energy of the peak of the well resonance is always e2/ π hbar (two spin states included) for the well at the center of the barrier;
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74
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33750651764
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it is independent of the strength of the coupling (so long as it is small) between the well state and the electrode states. In our case, however, where the coupling is not small, the actual coupling strength does affect the conductance. This fact is discussed using a simple test case in footnote 16 of
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(1987)
Phys. Rev. B
, vol.36
, pp. 8173
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Lang, N.D.1
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75
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84928001949
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The essence of a chemical bond between atoms or between an atom and a surface is that the coupling is not small, i.e., that it is not capable of being treated perturbatively.
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76
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84928001948
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The peak in the local density of states that can be associated with pxy states is narrower on the center Al atom in the three-atom linear chain than on the end atoms. This supports the contention that the overlap between 3pxy orbitals on the atom is larger with states of the metal than with these same orbitals on an adjacent Al atom.
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77
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0002256430
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We take the bond length between the surface and the S atom (measured from the S nucleus to the positive-background edge of the electrode) to be fixed at 1.9 bohrs, which is the calculated bond distance for the case in which nothing else is bonded to the atom [see, ]. We take the S-Al bond length to be 4.4 bohrs, which is the measured distance in beta-AlS32 crystals: R. W. G. Wyckoff, Crystal Structures (Interscience, New York, 1964), Vol. 2.
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(1985)
Surf. Sci.
, vol.150
, pp. 24
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Lang, N.D.1
Holloway, S.2
Nørskov, J.K.3
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78
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84928001947
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This asymmetry has a substantial effect in scanning tunneling microscopy studies of individual adsorbed S atoms.
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