Spinfree formulation of reduced density matrices, density cumulants and generalised normal ordering
Spinfree formulation of reduced density matrices, density cumulants and generalised normal ordering
复制标题
约简密度矩阵、密度累积量和广义正态排序的无旋转公式
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
D. Mukherjee
中科院分区：
文献类型：
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作者：
W. Kutzelnigg;K. R. Shamasundar;D. Mukherjee
The k-particle reduced density matrices γ k for a singlet state or a spin-orientation averaged ensemble are invariant under the spin rotation group SU(2), i.e. they are independent of spin, even if they are expressed in terms of spin orbitals. The γ k contain the same information as their spinfree counterparts Γ k expressed in terms of spinfree orbitals. However, the relation between the two quantities is, by no means, elementary. The summation over spin is particularly demanding and surprisingly complicated for the k-particle density cumulants λ k and for the formulation of a generalised normal ordering with respect to an arbitrary reference state, including the generalised Wick theorem. Plausible extrapolations from small k turned out to be unjustified and some published expressions for k = 4 need to be revised. A compact general result, valid for all k has not yet been found.
