Mixed-gen Session 3: Quantum Monte Carlo
Online meeting - hosted by CECAM-HQ
This is the third of a series of on line events aimed mainly at PhD students and researchers in their first post-doc. Our goal is to provide a new venue for these young scientists to share their work, get expert feedback and have an opportunity to strengthen scientific relations within the CECAM community.
The event is fully on line and will have two parts. In the first, broadcasted as a Zoom webinar, Prof. David Ceperley, University of Illinois, will present a general talk in the area of Quantum Monte Carlo (title and abstract below). This will be followed by seminars given by two young members of the community to describe their work in the same area. In the second part of the event, we shall move to a virtual poster session hosted in a Gather room where more PhD students and researchers in their first post-doc will present pertinent projects. The session’s speaker and other (surprise) expert guests will join us for this poster session to discuss exciting new science.
If you are a PhD student or a post-doc:
Please use the Participate Tab on this page to start the application. You will have to login using your CECAM account to access the application form. If you don't have a CECAM account yet, use the register option on the top right corner of the login page...and welcome to CECAM!
If you are a more senior scientist:
Please contact the organisers and we shall process your registration.
Submission of posters
(Please note that - at least for the time being - we shall accept posters only from PhD students or researchers in their first post-doc)
After your application is accepted, you will be able to submit a poster. In the CECAM page for this event, go to “My participation” tab and click on “Add a poster”, providing in particular title and abstract following the recommended format. On the same form you can already upload your poster file in png or jpg if ready. These formats are strict to enable showing of the poster in the Gather session. If the poster file is not ready at the moment of submitting your abstract, you can upload it later by editing your submission (Go to “My participation” tab and click three vertical dots on “Actions” column on table “My posters”). Please upload your poster as soon as possible to enable a decision from the selection committee - see below.
Please note that posters will be visible on the Gather room associated with this session until the end of the series (July 2021) unless otherwise requested.
DEADLINE FOR SUBMISSION: TEN DAYS BEFORE THE EVENT
Selection of posters
Posters will be selected by the event organisers with the support of our main speaker and experts who will take place in the poster session.
Selection of the two talks by PhD or first year postdocs
These contributions, to be broadcasted in the Zoom webinar in the first part of the event, will be selected, after a preliminary screening by the organisers, the main speaker and guest experts, via a lottery from the posters selected for the Gather session. Please indicate in your application if you DO NOT WANT your poster to be considered for this lottery.
THE DECISION ON THE POSTER AND THE OUTCOME OF THE LOTTERY SELECTION WILL BE COMMUNICATED ONE WEEK BEFORE THE EVENT
POSTER SUBMISSIONS BEYOND THIS DEADLINE WILL BE ACCEPTED BUT NOT CONSIDERED FOR UPGRADE TO TALK. SUBMISSION WILL BE DEFINITELY CLOSED FOUR DAYS BEFORE THE EVENT.
SESSION 3. Title and abstract of talks
Simulating quantum systems
David Ceperley, University of Illinois Urbana-Champaign
In this talk I will present an overview of quantum Monte Carlo methods which have been used to simulate many-body continuum systems, with emphasis on the Diffusion Monte Carlo and the Path Integral Monte Carlo methods and their applications to the Wigner Crystal, superfluid helium and dense hydrogen.
Prospects of Forces and Geometry Optimization with Quantum Monte Carlo
Juha Tiihonen, Oak Ridge National Laboratory
Quantum Monte Carlo methods (QMC) describe the potential energy surface (PES) of strongly correlated structures with high accuracy and efficiency. However, the QMC forces face challenges due to systematic biases and statistical cost, which can be controlled but not fully mitigated with state-of-the-art estimator techniques. We show novel scaling relations of QMC force variances with the effective valence charge Zeff, along with an outlook of how large and heavy systems might be within reach for the modern applications of the QMC forces .
Additionally, we present a novel energy minimization technique  to relax multiple structural parameters using sparse sampling of the DMC PES. It uses density functional theory as a surrogate to obtain the optimal, the most rapidly converging line-search directions in the reduced parameter space. Resampling techniques are used on the surrogate model to predict and further minimize the computational cost of the DMC PES search. The approach can be generalized to any method preferring accurate and possibly noisy PES rather than forces. We present examples of the method as applied to flake-like 2D molecules and 2D monolayers.
 J. Tiihonen, R. C. Clay III, and J. T. Krogel, Towards Quantum Monte Carlo Forces on Heavier Ions: Scaling Properties, in preparation (2021)
 J. Tiihonen, and J. T. Krogel, Surrogate Hessian Accelerated Structural Optimization, in preparation (2021)
*This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, as part of the Computational Materials Sciences Program.
Quantum Monte Carlo determination of the principal Hugoniot of deuterium
Michele Ruggeri, CNRS, Maison de la Simulation
We show Coupled Electron Ion Monte Carlo results for the determination of the principal Hugoniot of deuterium. Particular care is given to the determination of the reference initial state, as well as to the evaluation of the influence of finite temperature and nuclear quantum effects on the computed Hugoniot curve. Our QMC results are in agreement with experimental data in low T, P conditions, while at higher T, P the computed Hugoniot is still more compressible than experimentally observed.
M. Ruggeri, M. Holzmann, D. Ceperley, C. Pierleoni, Phys. Rev. B, 102, 144108 (2020)
Sara Bonella (CECAM HQ) - Organiser
Ignacio Pagonabarraga (CECAM HQ) - Organiser