FASTcorrelation

The development of quantum mechanics in the first part of the 20th century has had profound implications for the understanding of matter on the microscopic scale. Starting only from the chemical composition, quantum mechanics, through the solution of the Schrödinger equation, can describe the properties of molecular or extended systems, such as the structure, elasticity, electrical properties, optical absorption, and many more. Together with the invention of computers and the introduction of suitable approximations and algorithms, this concept has led to the development of several general purpose methodologies to compute the properties of materials from first principles. Because of the complexity of the electronic correlation problem, the numerical methods available today solve the Schrödinger equation by approximating the electronic correlation contribution and require a compromise between accuracy and scalability to treat large systems (up to hundreds or thousands of atoms). The goal of the FASTcorrelation project is to develop and apply new powerful theoretical tools to compute the properties of materials from first principles by using quantum mechanics. The need for a breakthrough in this field is particularly urgent to accurately understand and predict the microscopic mechanisms and interactions involved in complex experimental and technological applications. For example, the weak dispersion forces necessary to understand the interactions in molecular crystals or in surface catalysis applications are poorly described by the commonly used ground state density functional methods. Other applications that require better theoretical descriptions involve electronic excitations such as, for example, the optimization of light absorption and electronic transfer in next generation solar cells. This proposal will address these different problems, involving both electronic ground state and excited state processes, within the same framework. The proposed theoretical and methodological development will build on the concept of linear response function (i.e. dielectric matrix or polarizability). Polarizability and dielectric matrix describe the response of electrons to an external perturbing potential and are intimately related to the problem of the electronic correlation, since each electron can be seen as an external perturbation acting on all the other electrons in the system. By systematically seeking better approximations of linear response functions, this proposal will, at the same time, improve the accuracy of the ground state correlation energy through the adiabatic connection fluctuation dissipation theorem and the description of excited states within Green’s function based methods. In combination with the powerful algorithms recently developed by the project coordinator, the proposed research will lead to revolutionary approaches to treat, with unprecedented accuracy, realistic models with hundreds of atoms and address within the same framework molecules, solids and nanostructures. A series of applications will also be explored, including molecular crystals and materials used in catalysis and solar cells. Such applications of high scientific and technological relevance will help test the accuracy of the new methodologies and demonstrate their computational efficiency. By developing a new general framework for first principles calculations and applying it to systems of significant technological interest, the outcomes of this proposal will have profound implications for science and society.