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小木虫论坛-学术科研互动平台 » 计算模拟区 » 第一性原理 » QE(Pwscf) » 【分享】ESPRESSO小组刚写的总结性文章
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wuli8

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freshgirl(金币+1,VIP+0):谢谢参与~ 7-24 23:15
http://d.namipan.com/d/QUANTUM%2 ... 65420e81bf136d60600
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21楼2009-07-24 11:54:52
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xirainbow

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freshgirl(金币+1,VIP+0):谢谢参与~ 7-24 23:15
熟悉ESPRESSO的朋友都知道赝势文件的后缀是UPF
我以前以为UPF是ultro-soft-pseudo的缩写
所以一直很纳闷为什么后缀是UPF的赝势中既有超软，又有模守恒

今天看这篇文献，终于知道了UPF的全称是Unified Pseudopotential File (UPF).

ESPRESSO如是说：“Another problem affecting interoperability of PW-PP codes is the availability of data files containing atomic PP’s — one of the basic ingredients of the calculation. There are many different types of PP’s, many different codes generating PP’s (see e.g. Ref [75, 76, 77]), each one with its own format. Again, the choice has fallen on a simple solution that makes it easy to write converters from and to the format used by QUANTUM ESPRESSO. Each atomic PP is contained in a formatted file (efficiency is not an issue here), described by a XML-like syntax. The resulting format has been named Unified Pseudopotential File (UPF). Several converters from other formats to the UPF format are available in QUANTUM ESPRESSO.”

[ Last edited by xirainbow on 2009-7-24 at 21:09 ]
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22楼2009-07-24 21:06:48
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xirainbow

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fegg7502(金币+2,VIP+0):thank you very much! 7-26 21:48
ESPRESSO从物理层面上是如何实现并行的呢？
共分为4个阶段：
1，image parallelizaton：将所有处理器分为n_image组image(每组中包含若干个image)。
2，pool parallelizaton：将每组中的处理器进而分为n_pool个pool，每个pool被用来处理若干个k点。
3，plane-wave parallelizaton：将每个pool中的处理器分为n_pw组。然后将实空间和倒空间中的网格分配给这n_pw组。
4，task-group parallelizaton：处理器进而再被分为n_task组。每一个组被用来处理一个电子态的组合。每一个电子态的组合将被用于傅立叶变换，而傅立叶变换在每一个n_task中式被并行化的。

我的翻译和学术水平太低，大家看起来会比较难受，那就直接看原文吧；）如果我上面写的有不妥之处，还请多多指正；P
“In this hierarchy, groups implementing coarser-grained parallel tasks are split into groups implementing finer-grained parallel tasks. The first level is image parallelization, implemented by dividing processors into nimage groups, each taking care of one or more images (i.e. a point in the configuration space, used by the NEB method). The second level is pool parallelization, implemented by further dividing each group of processors into npool pools of processors, each taking care of one or more k-points . The third level is plane-wave parallelization, implemented by distributing real- and reciprocal-space grids across the nPW processors of each pool. The final level is task group parallelization [79], in which processors are divided into ntask task groups of nFFT = nPW=ntask processors, each one taking care of different groups of electron states to be Fourier-transformed, while each FFT is parallelized inside a task group. A further paralellization level, linear-algebra, coexists side-to-side with plane-wave parallelization, i.e. they take care of different sets of operations, with different data distribution.”

[ Last edited by xirainbow on 2009-7-25 at 11:55 ]
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23楼2009-07-25 11:54:18
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xirainbow

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最近版本的ESPRESSO应该已经加入了PAW的赝势吧：）
“Both separable NC-PPs and US-PPs are implemented; recently,also the projector augmented-wave method [37] has been added, largely following the lines of Ref [84] for its implementation.

[ Last edited by xirainbow on 2009-7-26 at 16:47 ]
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24楼2009-07-26 16:38:48
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xirainbow

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fegg7502(金币+2,VIP+0):thank you very much! 7-26 21:48
US-PP的ecutwfc应该是ecutrho的6~12倍。
我记得以前曾在哪里看到过，ecutrho好像也需要进行收敛测试的。
关于下面的两组参数，我以前从没注意过。文章中也给出了相应的解释。
nr1, nr2, nr3         INTEGER
    three-dimensional FFT mesh (hard grid) for charge
    density (and scf potential). If not specified
    the grid is calculated based on the cutoff for
    charge density (see also "ecutrho"

nr1s, nr2s, nr3s         INTEGER
    three-dimensional mesh for wavefunction FFT and for the smooth
    part of charge density ( smooth grid ).
    Coincides with nr1, nr2, nr3 if ecutrho = 4 * ecutwfc ( default )
            
原文：In the case of US-PPs, the electronic wave functions can be made smoother at the price of having to augment their square modulus with additional contributions to recover the actual physical charge densities. For this reason, the charge density is more structured than the square of the wavefunctions, and requires a larger energy cutoff for its plane wave expansion (typically, 6 to 12 times larger; for a NC-PP, a factor of 4 would be mathematically sufficient). Hence, different real-space Fourier grids are introduced - a "soft" one that represents the square of electronic wave functions, and a "hard" one that represents the charge density [82, 85].
The augmentation terms can be added either in reciprocal space (using an exact but expensive algorithm) or directly in real space (using an approximate but faster algorithm that exploits the local character of the augmentation charges).

   Variable:       tqr

   Type:           LOGICAL
   Default:        .FALSE.
   Description:    If .true., use the (VERY EXPERIMENTAL) real-space algorithm
                   for augmentation charges in ultrasoft pseudopotentials.
                   Must faster execution of ultrasoft-related calculations,
                   but numerically less accurate than the default algorithm.
                   Use with care and after testing!

[ Last edited by xirainbow on 2009-7-27 at 19:30 ]
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25楼2009-07-26 16:51:58
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xirainbow

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fegg7502(金币+2,VIP+0):thank you very much! 7-26 21:48
晶体的对称性是自己加上的。这点跟MS是不一样。
Crystal symmetries are automatically detected and exploited to reduce computational costs, by restricting the sampling of the BZ to the irreducible wedge alone.

下面这句话，有点不明白。
When only the gama point (k = 0) is used, advantage is taken of the real character of the orbitals, allowing to store just half of the Fourier components.

用Fermi-Dirac smearing来考虑温度效应，以前看过一篇有关的计算。
The finite-temperature effects on the electronic properties can be easily accounted for by using the Fermi-Dirac smearing not as a mathematical device, but as a practical way of implementing the Mermin density-functional approach

三维晶体可以加宏观电场进行计算。但这个跟Berry phace有什么关系？
slab可以加齿装电场。
The effects of finite macroscopic electric fields on the electronic structure of the ground state can be accounted for either through the method of Ref [106, 107] based on the Berry phase, or (for slab geometries only) through a sawtooth external potential [108, 109].
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26楼2009-07-26 16:58:51
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xirainbow

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ATOMIC 模块：
atomic模块完成三项任务:
1) solution of the self-consistent all-electron radial Kohn-Sham equations (with a Coulomb nuclear potential and spherically symmetric charge density);
2) generation of NC PPs, of US PPs, or of PAW data-sets;
3) test of the above PPs and data-sets.

在生成赝势时，有三个全电子方程备选：
1) the non relativistic radial Kohn and Sham equations,
2) the scalar relativistic approximation to the radial Dirac equations  
3) the radial Dirac-like equations derived within relativistic density functional theory .

The generation of fully relativistic NC and US PPs including spin-orbit coupling effects is also available.
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27楼2009-07-27 13:05:12
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Neoo

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非常感谢！

[ Last edited by Neoo on 2011-3-24 at 22:27 ]
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28楼2011-03-24 22:26:27
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hookah

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送鲜花一朵
来自开发小组的东东，必须推荐啊！
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29楼2011-09-27 14:12:47
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改王之王

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这个要好好看一看…………
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30楼2011-09-27 19:49:02
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