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SUMMARY:Recent progress in the first-principles quantum Monte Carlo: New a
 lgorithms in the all-electron calculations and a workflow system for QMC o
 ptimizations - Kosuke Nakano
DTSTART:20190904T103000Z
DTEND:20190904T113000Z
UID:TALK128785@talks.cam.ac.uk
CONTACT:Angela Harper
DESCRIPTION:First-principles quantum Monte Carlo (QMC) techniques\, such a
 s variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo 
 (DMC)\, are among the state-of-the-art numerical methods used to obtain hi
 ghly accurate many-body wave functions. These methods are especially usefu
 l when tackling challenging cases such as low-dimensional materials[1] bec
 ause QMC is no longer dependent on any semi-empirical exchange-correlation
  functions. We have been intensively improving a QMC code "TurboRVB\," whi
 ch has been mainly developed by Prof. Sandro Sorella (SISSA)[2]. I am goin
 g to talk about two recent improvements in the QMC algorithm.\n\nThe first
  topic is about all-electron calculations. Although it is convenient to re
 place core electrons in QMC calculations as in DFT\, such replacement some
 times induces nontrivial biases. All-electron calculations in QMC are not 
 as widely used as in DFT because the computational cost scales with Z^5.5
 −6.5\, where Z is the atomic number. We have recently developed new algo
 rithms to drastically decrease computational costs of all-electron DFT (va
 lid only for QMC)[3]\, and all-electron lattice regularized diffusion mont
 e Carlo (LRDMC)[4\,5]. I will present basic ideas of the new algorithms an
 d show several applications such as a binding energy calculation of the so
 dium dimer[3]. \n\nThe second topic is about a workflow system for QMC opt
 imizations. We are currently developing a python wrapper for TurboRVB\, wh
 ich is called Genius-TurboRVB (g-turbo)\, in order to "automatize" the com
 plicated optimization procedure of a many-body wave function. The wrapper 
 also makes it much easier to prepare input files\, to analyze output files
 \, and to perform advanced calculations. I will present fundamental featur
 es and several applications of the wrapper\, for example\, a phonon disper
 sion calculation of a solid[6].\n\n[1] S. Sorella\, et al. Phys. Rev. Lett
 . 121\, 066402 (2018).\n\n[2] S. Sorella\, https://people.sissa.it/~sorell
 a/web\, accessed 4 August (2019).\n\n[3] K. Nakano\, et al. J. Chem. Theor
 y Comput. 15\, 4044-4055 (2019).\n\n[4] M. Casula\, et al. Phys. Rev. Lett
 . 95\, 100201 (2005).\n\n[5] K. Nakano\, et al. to be submitted to Phys. R
 ev. Lett.\n\n[6] K. Nakano\, et al. in preparation.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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