Janus Juul Eriksen

Now out in JCTC:

pubs.acs.org/doi/full/10....

On my end, thanks to @villumfonden.bsky.social, @novo-nordisk.bsky.social, and the Independent Research Fund Denmark for generous funding.

We believe our protocol will allow for a physically sound and efficient estimation of general effects related to bulk solvation, and we're currently working on extensions to heterogeneous system (in terms of solvation free energies) as well as applications beyond ground-state properties.

Our study reports chemically intuitive results for binding energies of water, ethanol, and acetonitrile that all display fast convergence with respect to the bulk size (here shown for the case of liquid water).

Our work thus enables a focus on perturbations to local electronic structures only, e.g., that of a central monomer, and we show how results naturally generalize from simple dimer models to extended bulks.

This is made possible by means of an exact decomposition of total energies from Kohn–Sham density functional theory into corresponding monomer energies, operating in a basis of spatially localized molecular orbitals.

Solvation Lies Within: Simulating Condensed-Phase Properties from Local Electronic Structures In transitions between different environmental settings, a molecular system inevitably undergoes a range of detectable changes, and the ability to accurately simulate such responses, e.g., in the form...

In collaboration with Filippo Lipparini in Pisa, we have just published a new preprint detailing a robust protocol for computing binding energies of individual monomers suspended in homogeneous condensed phases:

arxiv.org/abs/2601.08649

Kasper F. Schaltz, Jonas Greiner, Filippo Lipparini, Janus J. Eriksen: Solvation Lies Within: Simulating Condensed-Phase Properties from Local Electronic Structures https://arxiv.org/abs/2601.08649 https://arxiv.org/pdf/2601.08649 https://arxiv.org/html/2601.08649

Now out in @acs.org JCTC:

pubs.acs.org/doi/full/10....

Found a few typos. Where to report? 😜

New v2.0.0 of OpenTrustRegion now released. Please see the changelog for an account of all of the major changes:

github.com/eriksen-lab/...

Hovedløst ikke at sikre Den Danske Ordbog I en tid, hvor AI gør det sværere at skelne sandt fra falsk, er der akut brug for troværdige, offentligt tilgængelige opslagsværker. Det er uforståeligt, at Den Danske Ordbog er lukningstruet

Regeringen har ikke fundet midler til at sikre det digitale opslagsværk Den Danske Ordbog.
»I en tid, hvor fakta er til forhandling, og hvor kunstig intelligens gør det sværere at skelne sandt fra falsk, er der akut brug for troværdige, offentligt tilgængelige opslagsværker,« skriver Rasmus Elmelund

Det Unge Akademi: Her er vores fire ønsker til årets forskningsreserve - Altinget Den frie forskning svækkes, hvis politiske dagsordener styrer midlerne. Der er brug for rolige rammer, langsigtet vision og reelt frie midler. Ellers mister vi fremtidens gennembrud, innovation og vid...

I Det Unge Akademi har vi skrevet en ønskeseddel til årets forhandlinger af forskningsreserven. Læs med her:
www.altinget.dk/forskning/ar...

#compchem

Geometric Direct Minimization for Low-Spin Restricted Open-Shell Hartree–Fock Theory It has recently been shown that configuration state functions (CSFs) with local orbitals can provide a compact reference state for low-spin open-shell electronic structures, such as antiferromagnetic ...

Our first @uclchemistry.bsky.social paper is now out in @pubs.acs.org... Take a look for new advances in low-spin ROHF theory for complex spin coupling! #CompChem pubs.acs.org/doi/10.1021/...

Lektorer og adjunkt: Der er lang vej til åndelig oprustning, når regeringen undergraver landets kulturelle infrastruktur Kulturarvsinstitutioner som Den Danske Ordbog, Rigsarkivet og Det Kongelige Bibliotek er ikke luksus – de er fundamentet for vores fælles hukommelse og evne til at tænke kritisk.

Sammen med Thomas, @kristinabsimonsen.bsky.social og @panktroels.bsky.social fra Det Unge Akademi har jeg skrevet et debatindlæg i @politiken.dk om regeringens “åndelige oprustning” og de samtidige nedskæringer i den kulturelle infrastruktur.

Læs med her:
politiken.dk/debat/debati...

GitHub - eriksen-lab/opentrustregion: A Reusable Library for Second-Order Trust Region Orbital Optimization A Reusable Library for Second-Order Trust Region Orbital Optimization - eriksen-lab/opentrustregion

Code: github.com/eriksen-lab/...

On my end, thanks to @villumfonden.bsky.social & Independent Research Fund Denmark for generous funding.

As such, we believe our work on the OpenTrustRegion library has massive potential in making genuine and robust second-order methods widely applicable throughout our community. This is the first paper in a new Nordic collaboration with @idamaho.bsky.social & Susi Lehtola. More to come!

Our permissibly licensed implementation can be included within both free and open-source, academically licensed closed-source, and commercial software packages. In the study, we present examples of interfaces to three different codes, and we bid future interfaces and extensions most welcome.

To that end, our implementation guarantees robust convergence onto a local minimum in both SCF calculations and other types of applications, and we demonstrate the difference in speed to conventional methods to be negligible, even for relatively simple systems.

In our opinion, the risk of false convergences onto saddle points in applications of HF and KS-DFT is undeniably real for first-order (and even many second-order) solvers to all but the most simple of molecular systems. These can only be safely avoided by employing robust second-order optimization.

As examples, our study presents applications to ground-state self-consistent field (SCF) calculations as well as the spatial localization and symmetrization of molecular orbitals, and we further highlight a variety of other interesting use cases towards the end.

The OpenTrustRegion library is designed with an intention to be more versatile, more robust, and more reusable than any previously reported implementation of the second-order trust region method for general electronic-structure calculations.

A Reusable Library for Second-Order Orbital Optimization Using the Trust Region Method We present a reusable, open-source software implementation of the second-order trust region algorithm in the new OpenTrustRegion library. We apply the implementation to the general-purpose optimizatio...

New preprint online today - spearheaded by my very talented postdoc, Jonas - on a new reusable, open-source software implementation of the second-order trust region algorithm:

arxiv.org/abs/2509.13931

Here are some of the reasons why this library may be useful for a great many in our community. 👇

Which five papers have most inspired you scientifically? Here is Michele Parrinello's answer (in no particular order):

1.) A. Rahman, "Correlations in the Motion of Atoms in Liquid Argon", Phys. Rev. 136, A405 (1964).
doi.org/10.1103/Phys...

1/5

🚨 10 days left until deadline (14 Sept) 🚨

Et forsøg på åndsrustbekæmpelse. Regeringen melder i dag ud, at den vil afsætte 68 mio. kr. til at styrke tysk og fransk på landets videregående uddannelser:

ufm.dk/aktuelt/pres...

Fault-tolerant quantum computations of vibrational wave functions Quantum computation of vibrational properties of molecules is a promising platform to obtain computational advantages for computational chemistry. However, fault-tolerant quantum computations of vibra...

After a long time in the making I am happy that this piece of work finally sees the light of day: Fault-tolerant vibrational structure calculations

arxiv.org/abs/2508.16253

#compchem #compchemsky #quantum #quantumcomputing

The call is now live. Please see this thread for further information:

bsky.app/profile/janu...

The call is now live. Please see this thread for further information:

bsky.app/profile/janu...