CCP Flagship: Quasiparticle Self-Consistent GW for Next-Generation Electronic Structure

The engineering of materials to do new things, or take existing functionality and make it better, is the primary means by which society benefits from technology. The great majority of technological applications exploit some materials property that depends on how electrons interact with themselves and nuclei. How electrons behave, or the ``Electronic Structure'' is the key to understanding properties of materials at their most fundamental level. Electronic structure is a shorthand for what happens to electrons as a result of their interaction with other particles. We are able to understand and explain it by solving the fundamental equations of motion of quantum theory.

Until fairly recently direct solutions of these equations were too difficult, and most research was built around phenomenological models. The situation began to change, gradually at first, but over the past 20 years or so has become a veritable flood: approximations have evolved that solve the fundamental equations quite generally ab initio, meaning from first principles without reference to models or experimental input. It is a very important, but little known fact, that the slow development of an ab initio framework to realistically solve the fundamental equations for real materials systems has had a dramatic impact, first in pure scientific disciplines, and now plays a central role in almost every branch of science and engineering.

We will build on a recent theory that is more advanced than standard methods used today. It is more complex but it surmounts many of their limitations and is applicable to a wider class of materials. It can predict a wide range of materials properties in a universal manner that no other electronic structure theory can equal. This project will raise our present capabilities to a new level of functionality.

The range of phenomena accessible to these theories is truly vast. Transport properties of graphene and bilayers with insulators such as MoS2; topological insulators; the new class of Fe superconductors; defect levels in photovoltaic materials; spintronic and multiferroic materials; defect formation energies and chemical heats of reaction in materials desired for energy or structural application; and in general spectroscopic data (measured in research facilities such as the Rutherford labs) whose interpretation requires a state-of-the-art first principles modelling code. These are a few examples, of priority areas in EPSRC. All are subjects of intensive research around the world. In all these cases, present-day theoretical treatments suffer from significant limitations that the proposed theory can surmount.

Society benefits in two ways from the outcomes of this research proposal. Society benefits firstly by improving peoples lives through better technology. As one concrete example, graphene is emerging as a wonder-material for use in many kinds of electronic applications. This CCP9 code will make it possible to describe in a uniform framework, the tools needed to model electron transport in graphene, which in turn can be fed into realistic device simulators, that enter into circuit design. As a second example, it is increasingly accepted that photovoltaic cells will play an increasingly important role in the U.K. economy as they displace fossil fuels. A new class of perovskite-based solar cells emerged last year which has caught the immediate attention of the entire PV community. We will provide a framework to make it possible to describe many of the microscopic processes (light absorption, transport) at a level that well surpasses the best of standard methods used today. Basic knowledge like this must be combined with other building blocks to understand how the devices work, so that they can be controlled and optimised. Indeed some early stages in both these areas have already been accomplished (see track record, and Walsh's Letter of Support). Superconductivity, plasmonics, spintronics, are some other examples.

The scope of technologies that benefit from electronic structure theory is already very large, encompassing significant fraction of all materials studied today. It is used to design materials with desired electronic, magnetic, optical, and structural properties. By turning a tool accessible only to specialists into a universal code, many more scientists and engineers in their respective specialisms will be able to take advantage of its functionality. This project provides a path to enable researchers to understand, or build models for many kinds of properties with considerably greater reliability and power than is possible today. It will also enable U.K. staff to develop unique professional skills.

Society also benefits through the competitive edge in technology this code will help to maintain. The UK has been at the forefront in developing community codes with the ability to simulate materials properties without recourse to models, by solving the underlying equations of quantum theory in materials from first principles. The current CCP9 flagship project aims at the construction of databases for computed materials properties, and tools to perform data mining on those vastly expanding repositories. Indeed the U.S. Department of Energy has recently acknowledged significant advantage the U.K. and Europe hold in this area, and is emphasising a need to build up a counterpart there.

The new, unified theory this code is built around does not suffer from the limitations inherent in today's standard methods. It can predict a wide range of materials properties in a universal manner that no other electronic structure theory can equal and bring the state of the art to a new level. The U.K. will develop a capability that is unique in the world.