Faster G0W0 implementation for more accurate material design

Traditional plane wave G0W0 calculation size is limited by two bottlenecks : the need to invert a large matrix (the dielectric matrix) and the need to carry out summations over a large number of electronic states (conduction states). The first bottleneck is caused by the choice of the basis in which the dielectric matrix is represented : traditional G0W0 implementations use a plane wave basis, which needs to be relatively large to properly describe the matrix. This talk will explain how a Lanczos basis can be generated to substantially reduce the size of the matrix. Also, the number of conduction bands needed to reach convergence in the summations is usually an order of magnitude larger than the number of valence bands. Here, the calculation of the conduction states is avoided by reformulating the summations into linear equation problems (Sternheimer equations), which also substantially reduces the computation time. Finally, we will discuss how the introduction of a model dielectric operator allows further speedup in the calculation of the dielectric matrix without introducing further approximation in the method. Results for silane, acenes and C60 will be presented