Adding the molecular dynamics functionality to the quantum Monte Carlo code CASINO
نویسندگان
چکیده
This report describes developments to the CASINO Quantum Monte Carlo code for enabling coupled Diffusion Monte Carlo (DMC) and Density Functional Theory (DFT) molecular dynamics simulations. The main objective of the work is to develop a scalable interface between CASINO and the PWscf code (which is part of Quantum ESPRESSO). CASINO will be modified with an algorithm based on re-weighting, level-cross checking and periodic Jastrow recomputation. An interface will also be developed for the data communication and transfer between PWscf and CASINO. Following are the outcomes of the work: • The interface between PWscf and CASINO was developed and is now provided through a file with a standard format containing: geometry, basis set, and orbital coefficients. • To improve the parallel efficiency of the DMC algorithm, the allocation and re-distribution of walkers (i.e. the list of current electron positions and various associated quantities related to the energy and wave function) between the cores was optimised by implementing asynchronous communication to overlap computation. • The work on parallel efficiency significantly improved the behaviour of CASINO. For a fixed target of 100 per core for a total walker population, linear weak scalability has been demonstrated for over 80,000 cores on the Jaguar Cray XT5 machine (1.75 petaFLOPS) at Oak Ridge National Laboratory. Furthermore, with 82,944 cores, CASINO version 2.7 is more than 30% faster than version 2.6 and the total cost of re-distributing walkers (including the DMC equilibration) was reduced from 412 seconds to 1 second. This means it will be possible to use CASINO on machines with more than 100,000 cores. • Further minor modifications were also made to the CASINO distribution including: multiple pseudopotentials for elements with the same atomic number, support for running multiple jobs simultaneously, faster partial-ranking algorithm, interface support for CRYSTAL09 and a major revision of the user manual. The developments have been introduced within the main CASINO (version 2.10) and PWscf (version 4.3) code bases. dCSE Final Report: DMC-MD calculations in casino N.Nemec and M.D. Towler
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