-
1
-
-
84926566896
-
-
Author to whom all correspondence should be addressed. Present address: Department of Chemistry and Biochemistry, University of California, Los Angeles, California, 90095 1569.
-
-
-
-
2
-
-
84926535475
-
-
Deceased.
-
-
-
-
60
-
-
84926540709
-
-
using a Heisenberg spin Hamiltonian with on site anisotropies to describe the magnetic interactions in solid oxygen, note that the ``...softness of the magnon energy spectrum in the β configuration, which causes a higher entropy with respect to the α phase,'' may be of crucial importance for the α β phase transition. Their results, however, are based in the spin wave approximation for classical spins, and a particular structure for the spins in the β phase was assumed.
-
-
-
-
65
-
-
84926550331
-
-
A. A. Radzig and B. M. Smirnov, Reference Data on Atoms, Molecules, and Ions (Springer Verlag, Berlin, 1985), p. 446.
-
-
-
-
66
-
-
84926552294
-
-
The value of the phenomenological Heisenberg interaction J used in the present work is defined as twice that used in the work of Stephens and Majkrzak, Ref. 25.
-
-
-
-
67
-
-
84926532069
-
-
A. J. R. da Silva and L. M. Falicov, in New Trends in Magnetic Materials and their Applications, edited by J. L. Morán López and J. M. Sánchez (Plenum, New York, 1994).
-
-
-
-
68
-
-
84926607128
-
-
The fact that in the calculated spectra of α and β oxygen the molecular Frenkel excitons are separated in energy from the charge transfer states is related to the size of the cluster. For the four molecule cluster the highest energy molecular exciton can only involve up to four Frenkel excitons, whereas in the solid there will be excitations composed of as many Frenkel excitons as the number of molecules. This would result in the overlap between the many molecular exciton states and the charge transfer band.
-
-
-
-
70
-
-
84926579583
-
-
A. J. R. da Silva, Ph.D. thesis, University of California, Berkeley, 1994.
-
-
-
-
71
-
-
84926558157
-
-
It should be noted that the total free energy cannot be obtained from the present small cluster calculation. The lattice contributions to the free energy (both to the internal energy and entropy) are not included in the model. Therefore, the α β phase transition temperature cannot be predicted. However, the low energy electronic excitations from the spectra in Figs. refa3 and refb3 can be used to estimate the magnetic contribution to the entropy. In particular, they can be used to calculate the magnetic entropy difference Δ Sβα(T) at the transition temperature, T = Tαβ = 23.9 K.
-
-
-
|
