Despite the success and widespread use of Density Functional Theory (DFT) in material sciences, the accurate determination of ground and excited state properties of complex systems requires in most cases models that go beyond DFT. These models are often based on many-body perturbation theory methods, such as Moller-Plesset perturbation theory (MP2), the Random Phase Approximation (RPA) and ab-initio GW method, which have emerged as the novel standard for the next generation first principle simulations. However, the successful application of these methods to large systems, with thousands of atoms, is a challenge due to the higher computational complexity.<br/>In this talk methodological and algorithmic improvements will be presented for two codes, CP2K and BerkeleyGW for the ground and excited state properties respectively.<br/>In CP2K we have developed a novel algorithm for MP2 and RPA correlation energies introducing the resolution-of-identity (RI) approximation within the Gaussian and Plane-Waves (GPW) approach, which allows to speed-up the computation by a factor 10-15 compared to the canonical implementations for MP2 and to reduce from O(N6) to O(N4) the computational effort for RPA. In addition to this, our implementation displays excellent parallel scalability up to tens thousands of processes, with the possibility of accelerating the computationally intense kernels by employing graphics processing units (GPU).<br/>In BerkeleyGW, within a canonical plane-waves (PW) GW approach, the combination of low-rank approximation and band compression methods allowed us to reduce the unfavorable computational cost due to the large size of the PW basis. These improvements have been combined with a multilevel parallel implementation with computational kernels specifically optimized for new many-core CPU architectures . In this way we have been able to scale BerkeleyGW to the full-Cori system at NERSC, utilizing an high fraction of peak performance and excellent time to solution .<br/>We have applied MP2 and RPA to study the properties of bulk water and GW to crystalline defect problems with up to 1000 atoms .

Large-scale MP2, RPA and GW calculations on pre-exascale HPC systems

254th National Meeting (2017)

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