## Condensed Matter Theory Group Meetings: Summer 18/19

This term’s meetings will take place at 11am on Thursdays. Please volunteer a talk or make known any masters students who are willing to give talks.

**Dice Seminars:**

Sometimes we run **Dice Seminars**, which occur over the course of 5 weeks or so, and consist of us collaboratively learning about a given topic, by reading a paper or paper section, and rolling a dice to determine who will talk about what they’ve read. The previous topic was “Topological Insulators”, and ran for an extended period. The topic before that was “Weyl Semimetals”.

**Other Meetings:**

There are ~weekly condensed matter seminars at 3pm on Fridays**, **which will be interesting for anyone attending our group meetings. These are advertised internally.

**Mailing List:**

If you would like to be added to the mailing list for these meetings, please **subscribe** or contact Ryan or Marcin (addresses at page footer).

Week | Presenter | Talk | Venue |

23 9th May | TBR (To Be Rolled) | Dice seminar – machine learning weeks 9-11 | C36 |

25 23rd May | Henning Schomerus | C36 | |

26 30th May | Neil Drummond | Adhesion of graphene to hexagonal boron nitride and gold | C36 |

27 6th June | David Thomas | Defect Formation Energies in Graphene | C36 |

28 13th June | Marcin Szyniszewski | Entanglement transition from variable-strength weak measurements | C36 |

29 20th June | Ryan Hunt & Yassmin Asiri | A7 | |

30 27th June | Tom Simons | C36 | |

SV4 25th July | Tim Jansen | An atom in Jellium | C36 |

SV9 29th August | Dr. Nakano | QMC and the “TurboRVB” code Abstract below | C36 |

Talks for next term: Alessandro Romito, Gabriel Bean, Marcin Szyniszewski

## Abstracts

**Dr. Nakano – QMC and the “TurboRVB” code**

First-principles quantum Monte Carlo (QMC) techniques, such as variational quantum Monte Carlo (VMC) and diffusion quantum Monte Carlo (DMC), are among the state-of-the-art numerical methods used to obtain highly accurate many-body wave functions. These methods are especially useful when tackling challenging cases such as low-dimensional materials[1] because QMC is no longer dependent on any semi-empirical exchange-correlation functions. We have been intensively improving a QMC code “TurboRVB,” which has been mainly developed by Prof. Sandro Sorella (SISSA)[2]. I am going to talk about two recent improvements in the QMC algorithm.

The first topic is about all-electron calculations. Although it is convenient to replace core electrons in QMC calculations as in DFT, such replacement sometimes 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 algorithms to drastically decrease computational costs of all-electron DFT (valid only for QMC)[3], and all-electron lattice regularized diffusion monte Carlo (LRDMC)[4,5]. I will present basic ideas of the new algorithms and show several applications such as a binding energy calculation of the sodium dimer[3].

The second topic is about a workflow system for QMC optimizations. We are currently developing a python wrapper for TurboRVB, which is called Genius-TurboRVB (g-turbo), in order to “automatize” the complicated 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 features and several applications of the wrapper, for example, a phonon dispersion calculation of a solid[6].

[1] S. Sorella, et al. Phys. Rev. Lett. 121, 066402 (2018).

[2] S. Sorella, https://people.sissa.it/~sorella/web/, accessed 4 August (2019).

[3] K. Nakano, et al. J. Chem. Theory Comput. 15, 4044-4055 (2019).

[4] M. Casula, et al. Phys. Rev. Lett. 95, 100201 (2005).

[5] K. Nakano, et al. to be submitted to Phys. Rev. Lett.

[6] K. Nakano, et al. in preparation.