[molpro-user] precision problems in calculationg Hessian matrix

张世扬 zhangshiyang04 at mails.tsinghua.edu.cn
Mon Oct 22 08:49:04 BST 2007

When we calculate harmonic vibration frequencies and normal modes, the default step size of the numerical differentiation of the energy is rstep=0.001 [bohr]. And the default convergence threshold for energy is 1.d-6. In this case, we cannot get precision of Hessian matrix as the output file shows to us. Why the elements of Hessian matrix in the molpro output file can achieve this precision?   

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