Comparison of calculation methods for the tunnel splitting at excited states of biaxial spin models
Cui Xiao-Bo (崔晓波)a, Chen Zhi-De (陈芝得)b
a Department of Physics and Institute of Modern Condensed Matter Physics, Guangzhou University, Guangzhou 510405, China; b Department of Physics, Jinan University, Guangzhou 510632, China
Abstract We present the calculation and comparison of tunnel splitting at excited levels of biaxial spin models by various methods, including the generalized instanton method, the generalized path integral method for coherent spin states, the perturbation method, and the exact method by numerical diagonalization of the Hamiltonian. It is found that, for integer spin with spin number around 10, tunnel splitting predicted by the generalized path integral for coherent spin states is about $10^{-n}$ times of the exact numerical result for the nth excited level, while the ratio of the results of the perturbation method and the exact numerical method diverges in the large spin limit. We thus conclude that the generalized instanton method is the best approximate way for calculating tunnel splitting in spin models.
Received: 15 January 2003
Revised: 09 December 2003
Accepted manuscript online:
Cui Xiao-Bo (崔晓波), Chen Zhi-De (陈芝得) Comparison of calculation methods for the tunnel splitting at excited states of biaxial spin models 2004 Chinese Physics 13 1124
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