*(Cross-post from our report published in the Psi-k blog)*

From 20th until 24th June 2022 I co-organised a workshop on the theme of
Error control in first-principles modelling
at the CECAM Headquarters in Lausanne
(workshop website).
For one week the workshop unified like-minded researchers from a range of communities,
including quantum chemistry, materials sciences, scientific computing and
mathematics to jointly discuss the determination of errors in atomistic
modelling. The main goal was to obtain a cross-community overview of ongoing
work and to establish new links between the disciplines.

Amongst others we discussed topics such as: the determination of errors in
observables, which are the result of long molecular dynamics simulations, the
reliability and efficiency of numerical procedures and how to go beyond
benchmarking or convergence studies via a rigorous mathematical understanding of errors.
We further explored interactions with the field of uncertainty quantification to link
numerical and modelling errors in electronic structure calculations or to
understand error propagation in interatomic potentials via statistical
inference.

## Organisers

## Participants

A primary objective of the conference was to facilitate networking and exchange
across communities. Thanks to the funds provided by CECAM and Psi-k we managed to
get a crowd of 30 researchers, including about 15 junior researchers, to come
to Lausanne in person. Moreover we made an effort to enable a virtual
participation to the smoothest extent possible. For example we provided
a conference-specific Slack space, which grew into a platform
for discussion involving both in-person as well as virtual participants
during the conference.
In this way in total about 70 researchers from 18 countries could participate in
the workshop. The full list of participants is available
on the workshop website.

## Workshop programme

The workshop programme was split between the afternoon sessions, in which we
had introductory and topic-specific lectures, as well as the morning sessions,
which were focussed on informal discussion and community brainstorming.

### Afternoon lectures

##### Monday June 20th 2022

*Uncertainty quantification for atomic-scale machine learning.* (Michele Ceriotti, EPFL)

[slides]
[recording]
*Testing the hell out of DFT codes with virtual oxides.* (Stefaan Cottenier, Ghent University)

[slides]
[recording]
*Prediction uncertainty validation for computational chemists.* (Pascal Pernot, Université Paris-Saclay)

[slides]
[recording]
*Uncertainty driven active learning of interatomic potentials for molecular dynamics* (Boris Kozinsky, Harvard University)

[recording]
*Interatomic Potentials from First Principles* (Christoph Ortner, University of British Columbia)

[slides]
[recording]

##### Tuesday June 21st 2022

*Numerical integration in the Brillouin zone* (Antoine Levitt, Inria Paris)

[slides]
[recording]
*Sensitivity analysis for assessing and controlling errors in theoretical spectroscopy and computational biochemistry* (Christoph Jacob,

TU Braunschweig)

[slides]
*Uncertainty quantification and propagation in multiscale materials modelling* (James Kermode, University of Warwick)

[slides]
[recording]
*Uncertainty Quantification and Active Learning in Atomistic Computations*

(Habib Najm, Sandia National Labs)
*Nuances in Bayesian estimation and active learning for data-driven interatomic potentials for propagation of uncertainty through molecular dynamics*

(Dallas Foster, MIT)

[slides]
[recording]

##### Wednesday June 22nd 2022

*The BEEF class of xc functionals* (Thomas Bligaard, DTU)

[recording]
*A Bayesian Approach to Uncertainty Quantification for Density Functional Theory* (Kate Fisher, MIT)

[slides]
[recording]
*Dielectric response with short-ranged electrostatics* (Stephen Cox, Cambridge)

[slides]
*Fully guaranteed and computable error bounds for clusters of eigenvalues* (Genevieve Dusson, CNRS)

[slides]
[recording]
*Practical error bounds for properties in plane-wave electronic structure calculations* (Gaspard Kemlin, Ecole des Ponts)

[slides]
[recording]
*The transferability limits of static benchmarks* (Thomas Weymuth, ETH)

[slides]
[recording]

##### Thursday June 23rd 2022

*An information-theoretic approach to uncertainty quantification in atomistic modelling of crystalline materials* (Maciej Buze, Birmingham)

[slides]
[recording]
*Hyperactive Learning* (Cas van der Oord, Cambridge)

[slides]
[recording]
*Benchmarking under uncertainty* (Jonny Proppe, TU Braunschweig)
*Model Error Estimation and Uncertainty Quantification of Machine Learning Interatomic Potentials* (Khachik Sargsyan, Sandia National Labs)

[slides]
[recording]
*Committee neural network potentials control generalization errors and enable active learning* (Christoph Schran, Cambridge)

[slides]
[recording]

### Morning discussion sessions

The discussion sessions were centred around broad multi-disciplinary topics to
stimulate cross-fertilisation. Key topics were active learning techniques for
obtaining interatomic potentials on the fly as well as opportunities to connect
numerical and statistical approaches for error estimation.

A central topic of the session on Thursday morning was the development of a
common cross-community language and guidelines for error estimation. This
included the question how to establish a minimal standard for error control and
make the broader community aware of such techniques to ensure published results
can be validated and are more reproducible. Initial ideas from this discussion are
summarised in a public github repository.
With this repository we invite everyone to contribute concrete examples of the
error control strategies taken in their research context. In the future we hope
to community guidelines for error control in first-principle modelling based on
these initial ideas.

## Feedback from participants

Overall we received mostly positive feedback about the event. Virtual
participants enjoyed the opportunity to interact with in-person
participants via the zoom sessions and Slack. For several in-person
participants this meeting was the first physical meeting since the pandemic and
the ample opportunities for informal interchange we allocated in the
programme (discussion sessions, poster sessions, social dinner, boat trip
excursion) have been much appreciated.

A challenge was to keep the meeting accessible for both researchers from
foreign fields as well as junior participants entering this interdisciplinary
field. With respect to the discussion sessions we got several suggestions for
improvement in this regard. For example it has been suggested to (i) set and
communicate the discussion subject well in advance to allow people to get
prepared, (ii) motivate postdocs to coordinate the discussion, which would be
responsible to curate material and formulate stimulating research questions and
(iii) get these postdocs to start the session with an introductory presentation
on open problems.

## Conclusions and outlook

During the event it became apparent that the meaning associated to the term
“error control” deviates between communities, in particular between
mathematicians and application scientists. Not only did this result in a
considerable language barrier and some communication problems during the
workshop, but it also made communities to appear to move at different paces. On
a first look this sometimes made it difficult to see the applicability of
research results from another community.
But the heterogeneity of participants also offered opportunities to learn from
each other's viewpoint: for example during the discussion sessions we actively
worked towards obtaining a joint language and cross-community standards for
error control. Our initial ideas on this point are
available in a public github repository,
where we invite everyone to participate via opening issues and pull requests to continue
the discussion.