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奮力拼搏至尊木蟲(chóng) (文壇精英)
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[求助]
請(qǐng)問(wèn)用CASTEP如何計(jì)算磁性物質(zhì)FeVSb的單點(diǎn)能?謝謝!
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| 用MS5.5中的CASTEP計(jì)算FeVSb的單點(diǎn)能;由于FeVSb是磁性物質(zhì),請(qǐng)問(wèn)應(yīng)該如何設(shè)置?十分感謝。!渴望得到高手的指教。! |

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至尊木蟲(chóng) (文壇精英)

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勾選Use formal spin as initial即可,表示用系統(tǒng)默認(rèn)的數(shù)值來(lái)作初值;不勾選的話,需要自己輸入Initial spin的數(shù)值,F(xiàn)e的話,2.0作初值就可以了。charge不管,你的體系有沒(méi)有帶電荷,默認(rèn)值就可以了。 Electronic——more——SCF——Density mixing中的charge和spin只有當(dāng)你把Electronic minimizer的算法選為Density mixing才會(huì)有,這樣的charge和spin是Density mixing算法中的參數(shù),系統(tǒng)默認(rèn)值一般即可。 |

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至尊木蟲(chóng) (文壇精英)

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至尊木蟲(chóng) (文壇精英)

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如果自己指定初始值的話,應(yīng)該是每個(gè)晶胞中的總數(shù) (per unit cell)。 CASTEP提供了兩種定義磁性的途徑,你現(xiàn)在打算采用的是第一種,如下: Spin polarization Magnetic systems can be studied by carrying out spin-polarized DFT calculations with CASTEP. This setting is recommended for transition metal oxides, certain inorganic surface studies, and metallic systems containing magnetic elements (Fe, Co, Mn, Ni). Spin-polarized CASTEP calculations are normally carried out with a variable magnetic moment. This procedure, however, does not guarantee finding the lowest energy state. DFT solutions can converge to a variety of local minima, so that the metastable states are found. The most commonly obtained solutions correspond to high spin and low spin states. The state generated by CASTEP depends on the initial magnetic configuration, since the solution is likely to converge to the nearest local minimum rather than to the global minimum. There are two ways of defining the initial magnetic configuration: either specify the total magnetic moment per unit cell, which gets uniformly distributed over the space, or provide detailed information on the absolute values and direction (up or down) of the spins for each atom in the unit cell. The former method can be used for relatively simple systems where only two solutions are expected (magnetic and non-magnetic). The latter method, which specifies the spin state of the atoms in the system, is more general and gives much more flexibility. It is possible to set up ferromagnetic, ferrimagnetic, or antiferromagnetic calculations to get different starting spin arrangements. To set up a spin-polarized calculation with a uniformly distributed initial magnetic moment Choose Modules | CASTEP | Calculation from the menu bar to display the CASTEP Calculation dialog. Select the Setup tab. Check the Spin polarized checkbox and uncheck the Use formal spin as initial checkbox. Specify an Initial spin value. To optimize the spin value, select the Electronic tab and click on the More... button to access the CASTEP Electronic Options dialog. Select the SCF tab. Uncheck the Fix occupancy checkbox and check the Optimize total spin checkbox. To set up a spin-polarized calculation with a specified ordering of atomic moments Note: Initial magnetic moments on atoms are treated correctly by CASTEP only when the density mixing scheme is used for electronic structure minimization. CASTEP will ignore atomic information and will use the uniformly distributed magnetic moment for the all bands or EDFT minimizers. The value of the total moment is determined by the sum of formal spins in the system. Set formal spins for the atoms. After setting the formal spins, find and impose the symmetry of the system. Choose Modules | CASTEP | Calculation from the menu bar to display the CASTEP Calculation dialog. Select the Setup tab. Check the Spin polarized and Use formal spin as initial checkboxes. Select the Electronic tab and click on the More... button to access the CASTEP Electronic Options dialog. Select the SCF tab. Select Density mixing as the Electronic minimizer setting. Uncheck the Fix occupancy checkbox and check the Optimize total spin checkbox. It is important to include a sufficient number of empty bands when optimizing the spin state. The default number of empty bands is 4, which means that the maximum accessible increase in the spin value is 8. A calculation that started with the low spin state will be extremely slow if the actual minimum found by CASTEP corresponds to the high spin state (although this is not the case when a calculation starts with high spin and converges to low spin). Note: CASTEP might fail to converge the SCF if the number of empty bands is insufficient to accommodate the high spin state, especially in a calculation with variable occupation numbers (metallic systems). 建議你仔細(xì)學(xué)習(xí)一下CASTEP的help文檔,里面的解釋比較權(quán)威。 |

至尊木蟲(chóng) (文壇精英)

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