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【原创】QUANTUM ESPRESSO: Introduction paper
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来源http://blog.sina.com.cn/s/blog_5f15ead20100dxu2.html 下面的内容是关于【分享】ESPRESSO小组刚写的总结性文章 [“http://muchong.com/bbs/viewthread.php?tid=1443058&fpage=1”]的一个总结。 谢谢期间多位虫子的支持：P At 25-6-2009, the ESPROESSO group wrote a introduction paper and submited to Journal of physics:Condenced Matter. The title of this paper is "QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials". I read it and get a lot of interesting knowledge about this software. 1: 由于ESPRESSO是开源的，因此有很多小组基于ESPRESSO分别编写自己的程序，用以拓宽ESPRESSO的计算范围。此文中列举了几个小组的工作At the time of the writing of the present paper, third-party scientific software available to the QUANTUM ESPRESSO users’ community include: yambo, a general-purpose code for excited-state calculations within many-body perturbation theory [166]; casino, a code for electronic-structure quantum Monte Carlo simulations [152]; want, a code for the simulation of ballistic transport in nanostructures, based on Wannier functions [167]; xcrysden, a molecular graphics application, especially suited for periodic structures [150]. The qe-forge portal is expected to burst the production and availability of third-party software compatible with QUANTUM ESPRESSO. Among the projects already available, or soon-to-be available, on qe-forge, we mention: SaX [154], an open-source project implementing state-of-the-art many-body perturbation theory methods for excited states; dmft [153], a code to perform Dynamical Mean-Field Theory calculations on top of a tight-binding representation of the DFT band structure; qha, a set of codes for calculating thermal properties of materials within the quasiharmonic approximation [168]; pwtk, a fully functional Tcl scripting interface to PWscf [169]. 2. ESPRESSO下一步的发展重点在于：一、激发态，二、GW方法（应该是格林函数方法）。我对第二个最为期待：）Many of the soon-to-come additions will deal with excited-state calculations within timedependent DFT (TDDFT [158, 159]) and/or many-body perturbation theory [160]. A new approach to the calculation of optical spectra within TDDFT has been recently developed [161], based on a finite-frequency generalization of densityfunctional perturbation theory [54, 55], and implemented in QUANTUM ESPRESSO. Another important development presently under way is an efficient implementation of GWcalculations for large systems (whose size is of the order of a few hundreds inequivalent atoms) [162]. The implementation of efficient algorithms for calculating correlation energies at the RPA level is also presently under way [163, 164, 165]. It is foreseen that by the time this paper will appear, many of these developments will be publicly released. 3. http://qe-forge.org/ QEforge 是ESPRESSO项目组设立的使用GForge组建的开发平台。 而GForge是一个基于Web的协同开发平台。它提供一组帮助你的团队进行协同开发的工具，如论坛，邮件列表等。用于创建和控制访问源代码管理库(如CVS，Subversion)的工具。GForge将自动创建一个源代码库并依据项目的角色设置进行访问控制。其它工具还包括：管理文件发布，文档管理，新闻公告，缺陷跟踪，任务管理等。 在这个网站上面可以看到很多小组正在开发新的项目，以及项目开始的时间，其中有蒙特卡洛、准粒子近似、格林函数还有含时微扰等：）从上面看，格林函数小组是2008-11-13 17:54注册的；） Group Name Register Time Quantum Monte Carlo 2009-05-26 17:40 QE+MBH 2009-05-07 16:24 PWTK 2009-04-08 14:21 Quasiharmonic Approximation 2009-03-26 23:55 DMFT 2009-02-11 17:03 Self-energies And eXcitations 2008-12-05 10:03 QE live distribution 2008-11-20 11:16 GW+Wannier 2008-11-13 17:54 TDDFPT 2008-11-12 13:45 GRID lattice dynamics 2008-10-23 18:19 Quantum ESPRESSO 2008-09-22 15:02 ESPRESSO这样描述这个工作平台："qe-forge provides, through a user-friendly web interface,an integrated development environment, whereby researchers can freely upload, manage and maintain their own software, while retaining full control over it, including the right of not releasing it. The services so far available include source-code management software (CVS or SVN repository), mailing lists, public forums, bug tracking facilities, download space, and wiki pages for projects’ documentation. qe-forge is expected to be the main tool by which QUANTUM ESPRESSO end users and external contributors can maintain QUANTUM ESPRESSO-related projects and make them available to the community. 4. 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.” 5. ESPRESSO从物理层面上是如何实现并行的呢？共分为4个阶段： i，image parallelizaton：将所有处理器分为n_image组image(每组中包含若干个image)。 ii，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。 iii，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。 iv，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；）“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.” 6. 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! 7. 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]. 8. 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. 9. 在附录中还对Self-consistency，Iterative diagonalization（Davidson,Conjugate-Gradient），Wavefunction extrapolation，Symmetry，Fock exchange进行了说明，但我没怎么看懂：( |
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