A busy week!

A lot happened in the group this week.

First it’s great to welcoming new postdoctoral research fellow Janus Eriksen to the group. Janus is self-funded through Independent Research Fund Denmark, and is joining the group after doing a Humboldt Fellowship with Jürgen Gauss in Mainz. Welcome to Bristol Janus!

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Project entos goes from strength to strength, and as an outline and place holder for a fuller description of what we are doing, there is now a brief note on chemRxiv.

And finally, we had a great group hike in the Mendip Hills, south of Bristol. The weather was disturbingly good.

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Callum (who organised it) had the honour of first reaching the “summit”. (I say “summit” because the altitude is about 300m or 1000 ft.)

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Most of the group (Peter was taking the photo) in some ruin we found.

 

Congratulations!

Congratulations to Tim Wiles, who passed his PhD viva yesterday, and becomes the first TMCS student to graduate from my group! Tim worked on the Unsöld correlation functional, which we’re now finding allows the construction of accurate DFT approximations with extraordinarily low self-interaction errors. More on that in an up-coming publication…

Congratulations also to former group member Mainak Sadhukhan, who just started a faculty position at the Indian Institute of Technology, Kanpur. Mainak worked in the group as a Royal Society Newton International Fellow, before moving on to work with Alexandre Tkatchenko in Luxembourg.

Welcome to new group members

We’re delighted to welcome Susannah Bourne-Worster and Zack Williams to the group!

Susannah just completed her DPhil with Prof Peter Hore at the University of Oxford, and was awarded a prestigious three-year fellowship by the Royal Commission for the Exhibition of 1851. She will be working on our project on understanding efficiency of energy transport in photosynthesis.

Zack completed year-one of the TMCS programme and has joined the group for his doctoral research. He will be picking up Tim’s project on correlation functionals using the Unsöld approximation.

Unsöld functional – a new hybrid functional for correlation

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There are about four or five distinct ingredients used in modern density functionals:

  • integrals of functions of the density and its gradients (GGAs, etc)
  • inclusion of the kinetic energy density in such expressions (meta-GGAs)
  • a fraction of exact Hartree–Fock exchange (or a length-scale-screened variant)
  • a contribution from a wavefunction-based correlation method like MP2 or RPA

Now there is another:

Tim Wiles and F R Manby, ‘Wavefunction-like Correlation Model for Use in Hybrid Density Functionals’, J. Chem. Theory Comput., Article ASAP, DOI: 10.1021/acs.jctc.8b00337.

In this paper we introduce the UW12 correlation functional:

  • an explicit functional of occupied orbitals (i.e. a functional  of the 1-RDM)
  • an F12-like model of dynamic electron correlation
  • can be self-consistently optimized in a straightforward way
  • most of the complicated stuff handled through familiar DFT quadrature
  • no double-summation over virtual orbitals, so fast basis-set convergence

This functional can be used as a viable (and hybrid) alternative to use of MP2 in double-hybrid functionals, as we demonstrate in this paper. Our hybrid XCH-BLYP-UW12 functional has only one parameter, and is competitive with more highly parameterised  double hybrids for reaction barrier test sets.

If you don’t have access and want to read the paper, just email Fred.

Congratulations to Tim for publishing this work!