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xirainbow

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[交流] 【分享】US-PP 带来的问题;)

http://blog.sina.com.cn/s/blog_5f15ead20100dwhe.html

        The price to pay for US-PP, however, is that the Fourier representation of the Kohn–Sham equation becomes more complicated.
        First, when the electron density is calculated we have to add back the part of the electron distribution which is represented by the difference between the solid and the dashed line in Figure1(the so-called augmentation charges).
       Second, due to the relaxation of the normconserving condition, the Bloch eigenstates will be not orthonormal anymore. An overlap matrix has to be introduced and the eigenvalue problem will transform into a generalized eigenvalue equation.
      Third, the nonlocal part of the pseudopotential becomes density–dependent.
      Fourth, due to these modification , additional terms in the force calculation have to be calculated. However, the gain in computational cost by lowering the plane wave cutoff energy outweigh in many cases the additional computational effort which is required by these modifications.
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