# Expanding the scope and scale of first-principles quantum-mechanical simulations with the ONETEP linear-scaling method on high performance computers

Lead Research Organisation:
Imperial College London

Department Name: Physics

### Abstract

Computer simulations play an important part in our society e.g. flight simulators allow pilots to be trained more cheaply and safely than in the air. In science and technology, computer simulation is a powerful tool for understanding and predicting complex processes in materials. Simulations are often used alongside conventional experiments, but they can also be used when experiments are too expensive or even impossible to perform, e.g. when studying materials in extreme conditions such as the high temperatures and pressures at the centre of the Earth.The turn of the last century saw the start of a scientific revolution with the discovery of quantum mechanics (QM). On very small scales, nature behaves in a radically different way from our everyday experience. If we were shrunk down to the size of an atom navigation would become very difficult, as the uncertainty principle says that it is impossible to know at the same moment precisely where you are and where you are going! In spite of this bizarre behaviour, QM is astonishingly accurate, and provides the foundation for all our science and technology.Such claims are of no use unless the equations of QM can be solved for problems of interest to scientists and engineers today. The challenge is that the equations are very complicated - even two electrons are too much for finding a solution on paper. In a way, QM has itself provided the answer as it led to the invention of the transistor and so to the computer. However, even on the fastest computers it is only possible to solve the equations of QM exactly for small molecules, whereas the systems of interest to scientists today involve many thousands. Even the rapid and relentless progress of computer technology cannot provide the whole answer, because of the scaling of the problem.The work needed to accomplish a certain task generally increases with its size e.g. the time taken to mow a lawn is proportional to its area: if you double the size of your garden it will take you twice as long. This is an example of linear scaling, but the effort involved in many tasks increases faster than this. Sorting a set of books or CDs into alphabetical order or arranging your hand in a game of cards usually scales as the square of the number of objects involved: if you triple the number it will take nine (three squared) times as long. There are some tasks which are much worse, such as solving the travelling salesman problem to find the quickest route to visit a given set of places. Adding one more location doubles the time it takes to solve. Even if you can solve the problem for three locations in one minute, just 22 will take you a whole year. Solving the equations of QM exactly scales like this. However, in the 1960s a significant leap forwards was made with the introduction of density-functional theory (DFT), for which Walter Kohn won the 1998 Nobel Prize in chemistry. The origin of the unfavourable scaling is that electrons are charged particles. Like charges repel, so one electron's trajectory depends on all the others', as it wants to avoid them. So solving the equations which describe these trajectories becomes much harder as more electrons are involved. But the remarkable result of DFT is that the physical properties of the whole system, the answers to the questions we want, do not depend upon the details of these individual trajectories, but only on the average. So a linear-scaling solution of the equations is possible, which promises dramatically to expand the scale of quantum simulations accessible.The aim of this work is to adapt a recently-developed linear-scaling DFT code called ONETEP to take advantage of recent developments in computer technology so that it runs efficiently on the most powerful computers now available. Harnessing the power of linear-scaling methods and modern computers will allow scientists to perform simulations based on QM for systems made of tens of thousands of atoms for the first time.

### Organisations

### Publications

Avraam P
(2011)

*Factors influencing the distribution of charge in polar nanocrystals*in Physical Review B
Avraam P
(2012)

*Fermi-level pinning can determine polarity in semiconductor nanorods*in Physical Review B
Hine N
(2009)

*Linear-scaling density-functional theory with tens of thousands of atoms: Expanding the scope and scale of calculations with ONETEP*in Computer Physics Communications
Hine N
(2012)

*Linear-scaling density functional theory simulations of polar semiconductor nanorods*in Journal of Physics: Conference Series*Linear-scaling density-functional theory with tens of thousands of atoms: Expanding the scope and scale of calculations with ONETEP*in Computer Physics Communications

Hine ND
(2011)

*Electrostatic interactions in finite systems treated with periodic boundary conditions: application to linear-scaling density functional theory.*in The Journal of chemical physics
Hine ND
(2010)

*Linear-scaling density-functional simulations of charged point defects in Al2O3 using hierarchical sparse matrix algebra.*in The Journal of chemical physics
Prentice JCA
(2020)

*The ONETEP linear-scaling density functional theory program.*in The Journal of chemical physicsDescription | The ONETEP code aims to enable the simulation of materials at the level of the behaviour of electrons so that insight into processes at this scale can be gained and the properties of new materials predicted. The task of solving the quantum-mechanical equations is formidable, and this project has enabled high performance computers with thousands of processors to be used efficiently to simulate tens of thousands of atoms. This enables much more realistic simulations to be performed. The research funded by this grant enabled further development of the parallelisation of the code to exploit the latest supercomputers. |

Exploitation Route | As new functionality is added to the ONETEP code, it becomes available to non-academic users through the Materials Studio package. The ONETEP code is available commercially from Accelrys Inc. as part of the Materials Studio suite of software used by academics and industrialists worldwide. Outcomes from this project thus feed directly into updates to that software. There is also a separate academic license available from Cambridge Enterprise. |

Sectors | Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Energy,Pharmaceuticals and Medical Biotechnology |

URL | http://www.onetep.org/ |

Description | Accelrys (now BIOVIA, part of Dassault Systèmes) is a leading scientific research and development software and service company. It has 1,300 customers including 29 of the top 30 pharma/biotech companies, 4 of the top 5 chemicals companies and the top 5 aerospace companies. In particular, it has an established position in the field of materials modelling and simulation currently based around the Materials Studio application. This provides a graphical interface to a wide variety of simulation software. In 2004, Accelrys adopted ONETEP as the flagship for a new Nanotechnology Consortium aimed at industrial and government partners, that ultimately attracted over 30 members worldwide. Members of the ONETEP Developers' Group (ODG) contributed to training events across Europe and the US and a new staff position at Accelrys was created to develop the interface of consortium software with Materials Studio. In 2008, after the end of the first phase of the consortium, ONETEP was launched as a new product within Materials Studio. Total revenue from ONETEP to date exceeds $2M from over 200 organisations worldwide. The licensing of intellectual property (IP) was handled by Cambridge Enterprise, which also facilitates the sale of inexpensive academic licenses worldwide and the administration of collaboration agreements between members of the ODG and other groups (industrial as well as academic) worldwide. The IP transfer agreements that have been put in place provided an efficient pathway for the improvements and new functionality generated by this award to be disseminated to customers of Accelrys through the Materials Studio interface. |

First Year Of Impact | 2004 |

Sector | Aerospace, Defence and Marine,Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Energy,Pharmaceuticals and Medical Biotechnology,Transport |

Impact Types | Economic |