关注：

1） 表面的定义，表面真是二维的吗？如果没有体相支撑的话， 如何理解皮之不存毛将焉附?

2） 获得表面的的实验及理论方法： 表面的切割方法，真空层的定义

3)  表面研究的实验方法；

4） 表面研究的理论方法与工具；

5） 表面有关的书籍

题记： 有关表面的N个问题

1） 什么是表面重构？  

2） 理论模拟中新鲜切割的表面、relaxed 表面的物理含义？

3） 晶体的解理面

4） 表面化学键的分析方法

1. 从表面能的定义当中可以窥见一斑

Surface energies γ were computed according to

  γ= 1/2A (E^slab-NE^bulk)

where A denotes the surface area at top and bottom of the slab,  N is the number of formula units in the slabmodel, and E^bulk refers to one equivalent of bulk q-GeO2.  【N取多大合适？】

  All slabs are stochiometricallyprecise (there are exactly two O atoms for each Ge), and so the γ’s areindependent of the constituent elements’s chemical potentials, other than in an“off-stoichimetric” case such as GeTe(111).

    We ascertained 【确定, 探知】convergence with regardto slab thickness, and these tests are collected in the ESI. 【需对slab 厚度进行收敛测试】

We also did tests holding a certain number ofatoms fixed in the interior of the slab, as in a recent surface study oflayered tellurides.【slab中表面以下部分原子固定不动，以模拟体相情形】Inwhat followings, we allowed all atoms in the slabs to relax unitl forces convergebelow 0.01 eV Å^-`.

2.理论研究方法

We report a ground-state DFT study here, but wewill additionally resort to ab initio molecular dynamics (MD) for two purposes.

   First ,the latter provide a reasonable cross-check for the stability of the computedstructures , as has been done before for silica surfaces; energetically unfavorable surfaces may betrapped in local minima but in this case quickly fall apart upon simulatedannealing by MD【calypso也有这个功能哈】

In return,if a structure stays unchanged during a reasonably along MD run at finitetemperature, this may be used as evidence for its stability.

  Second, these techniques can be specificallyused to search for new surface reconstructions, as has been demonstrated with  success before[24].

  Sophistication使复杂; 使精致

   In principle, we follow the methodology ofChen et al. as described in Ref24.  Temperatureswere rescaled to300 K at each simulation step using the Berendsen thermostat; here,we performed integration over 10 ps in time steps of 2fs. The MD simulationswere also done with VASP but with more economic basis sets (300 eV cutoff);after the MD runs, however, the so-obtained structures were fully relaxed usingthe methodology named above, such that all given surfaces energies andstructures are fully comparable.

3. 化学键pCOOP&pCOHP

分析      The chemical bonding in selectedstructural models was analysed using an overlap-based scheme well established in chemistryand beyond, which has , however, rarely found use in plane-wave DFT: we employthe crystalorbital overlap population (COOP) criterion of Hughbanks and Hoffmann,a periodic extension of the long-known Mullikenpartitioning scheme.

 pCOOP :

  Plane-wavebasis sets as used here are (intrinsically ) delocalized;   nonetheless, by suitable projection techniques,one may re-extract the converted chemical information.

 In thiscase, doing so yields the projected COOP (pCOOP),which is practically done asfollows:

  For theopimised structural models, single-point computations are done on reducedk-space grids (see ESI) which were checked to be converged for this purpose.

  The self-consistent wavefunctions are then projected via generalanalytical expressions onto a minimal basis set of contracted【收缩了的, 已定约的, 契约的】 Slatertype orbitals.

 This way, theband functions have been expressed in an LCAO basis suitable for bondinganalysis, and the latter is subsequently ortho-normalized 【正交化】using Lowdin’s technique.

 From theso-obtained LCAO coefficients, projected overlap and density-of-states matricesare built, affording the pCOOP(k) which is finally  integrated over reciprocal space and plottedalong the energy axis for easy visual interpretation.

  Integrating pCOOP(E) up to the Fermi levelyields a   bond population (counted inelectrons) that can be used as an indicator towards the bond strength, justlike with the famous “traditional “ COOP. 【怎样学导师的绝活或拿手本领】

  We have alsoattempted to use our related pCOHP technique whichwould lead, upon integration, to energies instead of bond populations; with  the present implementation, however, a ratherlarge charge spilling of ~26% was found due to the projection onto a minimalbasis

Intrinsical 【本质的, 固有的】

4. 关于 Square planar carbon-Also in Solids文章的审稿

石墨烯（Graphene）是一种由碳原子以sp²杂化轨道组成六角型呈蜂巢晶格的平面薄膜，只有一个碳原子厚度的二维材料^[1]。石墨烯一直被认为是假设性的结构，无法单独稳定存在^[1]，直至2004年，英国曼彻斯特大学物理学家安德烈·海姆和康斯坦丁·诺沃肖洛夫，成功地在实验中从石墨中分离出石墨烯，而证实它可以单独存在，两人也因“在二维石墨烯材料的开创性实验”为由，共同获得2010年]诺贝尔物理学奖^[2]。

石墨烯目前是世上最薄却也是最坚硬的纳米材料^[3]，它几乎是完全透明的，只吸收2.3%的光"^[4]；导热系数高达5300 W/m·K，高于碳纳米管和金刚石，常温下其电子迁移率超过15000 cm²/V·s，又比纳米碳管或硅晶体（monocrystalline silicon）高，而电阻率只约10^-6Ω·cm，比铜或银更低，为目前世上电阻率最小的材料^[5][1]。因为它的电阻率极低，电子跑的速度极快，因此被期待可用来发展出更薄、导电速度更快的新一代电子元件或晶体管。由于石墨烯实质上是一种透明、良好的导体，也适合用来制造透明触控屏幕、光板、甚至是太阳能电池。

石墨烯另一个特性，是能够在常温下观察到量子霍尔效应。

附：网络问答

随着温度的升高，SiC(0001)从900度的SiC(0001)(3×3)R30°结构
到1030度的SiC(0001)(√3×√3)R30°结构
再到1280度的SiC(0001)(6√3×6√3)R30°结构重构
这些重构表示什么呀？谢谢！

Q:::如果没有重构的表面晶胞参数为a, b.
则(√3×√3)R30° 表示重构表面晶胞为√3aa×√3b, 且相对未重构晶胞旋转30°.
(6√3×6√3)R30° 同样理解

简单理解就是表面原子的排列方式了变化，要想知道这几种形式是什么样的，可以看下LEED图谱

A:::

Si(100)表面有哪几种重构形式啊
非常丰富，比如：
2x1 重构，2x1 重构(buckled)
2x2 重构，2x2 重构(buckled)
4x2 重构(buckled)……
具体怎么输关于它的POSCAR文件
Si由于表面原子势垒较大，如果你直接搭建一个清洁表面做优化就想跑出这么丰富的重构来是不可能的。唯有一个办法，就是你自己设想一些重构的初始结构，比如你搭建一个2x1结构出来，具体怎么搭，就要好好的去读那些结构的位置，然后自己写出poscar来。
从你的提问我看出你好像还没怎么阅读文献，所以建议你首先好好读读si重构的文献，然后熟悉一般的表面结构怎么搭建，再来做这个复杂的si重构。只要你读懂了几个文献，应该是可以做出来的。完全靠问出来就不大可能呢:-)

附.需参考的书籍

(1）Theoretical surface science： A Microscopic perspective; springer, Berlin, Heidelberg, New York,2009