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gongchangjie金蟲 (正式寫手)
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【討論】討論一下,用ms計算系統(tǒng)能量問題 已有4人參與
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用ms計算系統(tǒng)能量問題,計算得出的能量值有三個, Final energy E=.... Final free energy E-TS=...... NB est.0K energy(E-0.5TS)=...... ,這三項各代表什么意思? 如果選擇系統(tǒng)最小能量,應該是那一項?謝謝,歡迎討論,拍磚 [ Last edited by gongchangjie on 2010-6-2 at 10:08 ] |
第一原理資料匯編 |

銅蟲 (著名寫手)
金蟲 (正式寫手)

金蟲 (著名寫手)
鐵桿木蟲 (著名寫手)
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help里有 The CASTEP output is as follows. The line Final energy, E = -861.8315373731 eV gives the Kohn-Sham energy, EKS, which ignores the entropy. However, it is the total Mermin free energy that is minimized by CASTEP and reported in the SCF cycles in the line Final free energy (E-TS) = -861.8315374521 eV If you were actually interested in the electronic states at some reasonable nonzero temperature, you would smear the Fermi level with a thermal (i.e., Fermi-Dirac) smearing method and the free energy reported by CASTEP would be the value you require. However, it is often the T = 0 K value that is required and the smearing is necessary to improve the convergence of the numerical algorithm. As the smearing ('temperature') is increased, the TS term increases and the free energy, EKS - TS, goes down. At the same time, as the entropy contributes more and more to the free energy, the electronic minimization pays less attention to the EKS term, so the final EKS increases. Because the dependence of the free energy and the Kohn-Sham energy on the smearing width is the same (to first order), averaging the two values gives a much better approximation to the T = 0 K result: NB est. 0K energy (E-0.5TS) = -861.8315374126 eV 下面兩個能量應該是因為smearing的原因 |
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