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buct2010金蟲 (正式寫手)
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[求助]
關(guān)于VASP手冊中兩個參數(shù)設(shè)置的問題,希望大家指點(diǎn)一下!
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(1)LMAXMIX (PAW贗勢的設(shè)置參數(shù)) An additional flag controls up to which l quantum number the onsite PAW charge densities are passed through the charge density mixer and written to the CHGCAR file: LMAXMIX = l The default is LMAXMIX=2. Higher l-quantum numbers are usually not handled by the mixer, i.e. a straight mixing is applied for them (the PAW on-site charge density for higher l quantum numbers is reset precisely to the value corresponding to the present wavefunctions). Usually, it is not required to increase LMAXMIX, but the following two cases are exceptions: • L(S)DA+U calculations require in many cases an increase of LMAXMIX to 4 (or 6 for f-elements) in order to obtain fast convergence to the groundstate. • The CHGCAR file also contains only information up to LMAXMIX for the on-site PAW occupancy matrices. When the CHGCAR file is read and kept fixed in the course of the calculations (ICHARG=11), the results will be necessarily not identical to a selfconsistent run. The deviations can be (or actually are) large for L(S)DA+U calculations. For the calculation of band structures within the L(S)DA+U approach it is strictly required to increase LMAXMIX to 4 (d elements) and 6 (f elements). 問題: 是不是這個參數(shù)只對LSDA+U 計(jì)算有用?那如果用HF(Hartree-Fock)方法的時候也需要增大它嗎(體系有d-f元素)? (2)LRPA (光學(xué)計(jì)算中的隨機(jī)相近似) LRPA = .TRUE. or .FALSE. Default: .FALSE. Usually local field effect are included on the Hartree level only (LRPA=.TRUE.). This means that cell periodic microscopic changes of the local potential related to the change of the Hartree potential are included. If LRPA= .FALSE., however, changes of the Hartree potential and the exchange correlation potential are included. This usually increases the dielectric constants. The final values for the dielectric matrix can be found in the OUTCAR file after the lines. MACROSCOPIC STATIC DIELECTRIC TENSOR (including local field effects in RPA (Hartree)) For LRPA=.FALSE. the dielectric matrix is written after the lines: MACROSCOPIC STATIC DIELECTRIC TENSOR (including local field effects in DFT) The dielectric constants without local field effects is always determined (irregardless of LRPA). The piezoelectric tensors and the Born effective charges as well as the ionic contributions the to dielectric tensor are only calculated for LRPA=.FALSE. 問題: 這個隨機(jī)相近似對于介電函數(shù)有什么影響?是不是可以理解為DFT計(jì)算的時候設(shè)置LRPA = .TRUE.;HF(Hartree-Fock)計(jì)算的時候設(shè)置LRPA = .TRUE.? [ Last edited by buct2010 on 2012-2-29 at 09:23 ] |
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