# Geometry Optimization

SCF 電子結構收斂 ► 若在這無法收斂 ► Oband DFT 要去動SCF相關的參數

## 步驟

1. SCF over (每一移動一個原子，就算一次SCF)
2. 算Force ►作用對象是原子
3. SCF重做一次
4. 算Stress應力為0 ► 作用對象為cell
5. BFGS若不收斂，則為GO state不收斂(但有SCF有收斂)
► 最常原因是因為E_cut不夠，尤其在動晶包 (請看Stress是否有小不下來的現象)

force 微分一次(energy對位置微分)，原子看force
stress 微分兩次，晶包看stress

(2018/02/06)

force 與總個(晶包，內容物)的受力相關(各方向等等)
stress (應變=>伸長量) 長度變化量/參考長度(總長) => “沒有單位”

## 精確度的影響因素

1. tolerance ► Q:如何判斷他的值該設多少? A:還是要看計算什麼物性來做決定。
2. stress
3. force

## TPSD (2 points steepest descent)

TPSD ► 2 points 兩點之意(始=>末)，若要做TPSD castep計算，則需把BFGS的字手動更改為TPSD。或者直接於GO more內做更改。

## Fractional coordinates

Real Lattice 是(直或橫)的為A、B、C向量，而是由 uA(向量)+vB(向量)+wC(向量)所組成。

0.449079*(0,0,8)
0.550921*(0,0,8)

# Other notes

DFT-D means Van-der_Waals.
lo-to ► 用於離子晶體計算，在左右移動上補計算

DFT ► 屬基態
dft-dispesion
constraint ► 適用於固定原子 (需打開勾選最下面)
restraint ► 適用於表面重構
BFGS delocalize internals自由度較小

# 極化率計算

1.電場(or電子)
2.離子

## 算極化率

(metal不可點選 因為計算電場若使用金屬 會有電流產生)

# 與計算材料相關及其他類型程式推薦

## OVITO

Description:

``````Molecular dynamics (MD), molecular statics and Monte-Carlo based simulations are nowadays standard methods for modeling materials with atomic-scale resolution.
Such atomistic simulation models generate three-dimensional atomic configurations or trajectories, which usually need to be further analyzed in order to generate new scientific insights.
Powerful analysis and visualization techniques play a key role in this process as simulated systems become larger and more complex.
Without the right software tools, key information would remain undiscovered, inaccessible and unused.
The task of visualization packages such as OVITO is to translate the raw atomic coordinates into a meaningful graphical representation and enable an interpretation by the scientist.

OVITO is a freely available visualization and data analysis software for atomistic datasets as output by large-scale molecular dynamics/statics and Monte-Carlo simulations.
Its name is an acronym for Open Visualization Tool, emphasizing that flexibility and extensibility were important goals in the development of this software.
``````

(截取官網Introduction)

## ASE

Description:

``````ASE is an Atomic Simulation Environment written in the Python programming language with the aim of setting up, steering, and analyzing atomistic simulations.
``````

## Quantum-Espresso

Description:

``````Quantum ESPRESSO is an integrated suite of Open-Source computer codes for electronic-structure calculations and materials modeling at the nanoscale.
It is based on density-functional theory, plane waves, and pseudopotentials.

Quantum ESPRESSO has evolved into a distribution of independent and inter-operable codes in the spirit of an open-source project.
The Quantum ESPRESSO distribution consists of a “historical” core set of components, and a set of plug-ins that perform more advanced tasks, plus a number of third-party packages designed to be inter-operable with the core components.
Researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

Quantum ESPRESSO is an open initiative, in collaboration with many groups world-wide, coordinated by the Quantum ESPRESSO Foundation.
Present members of the latter include Scuola Internazionale Superiore di Studi Avanzati (SISSA) , the Abdus Salam International Centre for Theoretical Physics (ICTP), the CINECA National Supercomputing Center , the Ecole Polytechnique Fédérale de Lausanne, the University of North Texas, the Oxford University.
Courses on modern electronic-structure theory with hands-on tutorials on the Quantum ESPRESSO codes are offered on a regular basis in collaboration with ICTP.
(Last updated Sep. 29, 2017)
``````

## Xcrysden

Description:

``````XCrySDen is a crystalline- and molecular-structure visualisation program.
The name of the program stands for Crystalline Structures and Densities and X because it runs under the X-Window environment.
It facilitates a display of isosurfaces and contours, which can be superimposed on crystalline structures and interactively rotated and manipulated.
It also possesses some tools for analysis of properties in reciprocal space such as interactive selection of k-paths in the Brillouin zone for the band-structure plots, and visualisation of Fermi surfaces.

The graphical user interface of XCrySDen was developed to provide an easy to use and learn interface.
Casual users should be able to exploit more than just the basic functionality without devoting more than a few hours of effort to the task of learning the use of the program.
XCrySDen also provides a (partial) graphical user interface for CRYSTAL ab initio program, and a visualization system for PWscf and WIEN2k and initio programs.
``````

(截取官網)

## lyx

Description:

``````LyX is a document processor that encourages an approach to writing based on the structure of your documents (WYSIWYM) and not simply their appearance (WYSIWYG).
LyX combines the power and flexibility of TeX/LaTeX with the ease of use of a graphical interface.
This results in world-class support for creation of mathematical content (via a fully integrated equation editor) and structured documents like academic articles, theses, and books.
In addition, staples of scientific authoring such as reference list and index creation come standard.
But you can also use LyX to create a letter or a novel or a theatre play or film script.

LyX is for people who want their writing to look great, right out of the box.
No more endless tinkering with formatting details, “finger painting” font attributes or futzing around with page boundaries.
You just write. On screen, LyX looks like any word processor; its printed output — or richly cross-referenced PDF, just as readily produced — looks like nothing else.

LyX is released under a Free Software/Open Source license, runs on Linux/Unix, Windows, and Mac OS X, and is available in several languages.
``````

(截取官網)

## VESTA

Description:

``````VESTA is a 3D visualization program for structural models, volumetric data such as electron/nuclear densities, and crystal morphologies. Some of the novel features of VESTA are listed below.
``````

(截取官網)

## Crystallography Open Database

Description:

``````Open-access collection of crystal structures of organic, inorganic, metal-organic compounds and minerals, excluding biopolymers.
``````

(截取官網)

## USPEX

Description:

``````USPEX (Universal Structure Predictor: Evolutionary Xtallography...and in Russian "uspekh" means "success" - owing to the high success rate and many useful results produced by this method) is a method developed by the Oganov laboratory since 2004.
The problem of crystal structure prediction is very old and does, in fact, constitute the central problem of theoretical crystal chemistry. In 1988 John Maddox wrote that:

"One of the continuing scandals in the physical sciences is that it remains in general impossible to predict the structure of even the simplest crystalline solids from a knowledge of their chemical composition solids such as crystalline water (ice) are still thought to lie beyond mortals' ken".

USPEX method/code solves this problem and is used by over 4000 researchers worldwide.
The First Blind Test of Inorganic Crystal Structure Prediction shows that USPEX outperforms other methods in terms of efficiency and reliability.
The method continues to be rapidly developed. In addition to crystal structure prediction, USPEX can work in other dimensionalities and predict the structure of nanoparticles, polymers, surfaces, interfaces and 2D-crystals.
It can very efficiently handle molecular crystals (including those with flexible and very complex molecules) and can predict stable chemical compositions and corresponding crystal structures, given just the names of the chemical elements.
In addition to this fully non-empirical search, USPEX allows one to predict also a large set of robust metastable structures and perform several types of simulations using various degrees of prior knowledge.

USPEX can also be used for finding low-energy metastable phases, as well as stable structures of nanoparticles, surface reconstructions, molecular packings in organic crystals, and for searching for materials with desired physical (mechanical, electronic) properties.
The USPEX code is based on an efficient evolutionary algorithm developed by A.R. Oganov's group, but also has options for using alternative methods (random sampling, metadynamics, corrected particle swarm optimization algorithms).
USPEX is interfaced with many ab initio codes, such as VASP, SIESTA, GULP, Quantum Espresso, CP2K, CASTEP, LAMMPS, and so on.
``````

(截取官網)