Psi-k is a wide network of European researchers — working closely with many friends and colleagues around the world – that is intended to help build cooperation in the field of computational electronic structure calculations, in particular for crystalline quantum systems whose wave function Ψ has an associated wave vector k defining its periodicity, hence the name. It is co-ordinated by a series of working groups from around Europe. It produces a monthly newsletter, organizes a major conference every five years, and allows researchers to email each other regarding job openings, events, and other topics of mutual interest. The network is also able to provide some degree of financial support for small workshops and schools, and for collaborative research visits.
MISSION: Psi-k is a Europe-based, worldwide network of researchers working on the advancement of first-principles computational materials science. Its mission is to develop fundamental theory, algorithms, and computer codes in order to understand, predict, and design materials properties and functions. Theoretical condensed matter physics, quantum chemistry, thermodynamics, and statistical mechanics form its scientific core. Applications encompass inorganic, organic and bio-materials, and cover a whole range of diverse scientific, engineering, and industrial endeavours. Key activities of Psi-k are the organization of conferences, workshops, tutorials and training schools as well as the dissemination of scientific thinking in society.
This new website — introduced in 2015 to replace a venerable old site that provided sterling service over many years — offers a much more flexible modern design and functionality and it is to be hoped that it will provide even more stimulus for collaboration and cooperation amongst its members. Instructions regarding how to use it are here.
Purpose: The purpose of the Psi-k Volker Heine Young Investigator Award is to recognize an individual for her or his outstanding computational work in any type of condensed-matter, materials, or nanoscience research involving electronic structure calculations. In 2018 there will be one award of 2500 Euro and four runner-up prizes of 500 Euro each. The prize is sponsored by Nature Publishing Group.
Regulations and Procedure:
1) Applicants may be of any nationality working anywhere in the world.
2) The applicant’s PhD certificate must not be dated more than 5 years before the first day of the joint CMD/DPG – EPS Conference (March 11, 2018). Those who have not yet completed a PhD can also apply.
3) Young investigators who wish to compete for the Psi-k Volker Heine Young Investigator Award 2018 must submit:
abstract (in the format of the abstracts for the conference)
two-page description making the case for her/his outstanding scientific contribution
extended CV (incl. list of publications and talks/posters)
evidence of satisfying the conditions of regulation (2) above.
These items must be submitted by email, as a pdf attachment, to the chairperson of Psi-k whose address is given below. It must be received not later than December 1, 2017. The abstract must also be submitted as a regular contribution to the CMD/DPG Conference.
4) The candidate must arrange for two confidential support letters to be sent directly by to the Psi-k chairperson (see below). These letters (sent by email) need to be received before December 1, 2017. One of the letters must certify that the candidate meets the requirements of regulations (2) above.
5) The Psi-k Trustees will select five finalists who will get an invitation to present their work at the CMD/DPG Conference (25 min. talk + 5 min. discussion). After these presentations, the award committee will select the award winner.
6) The award winner will receive her or his award of 2500 Euro and the four runner-up their prizes of 500 Euro each, together with a certificate, at a presentation on the Psi-k Scientific Get-Together during the conference.
Award Committee: The award committee will consist of selected invited speakers of the CMD/DPG Conference and three members of the Psi-k Trustees.
CECAM-HQ-EPFL, Lausanne, Switzerland, 26-29 September 2017
Organizers: Carlos L. Benavides-Riveros (Martin-Luther Universität Halle-Wittenberg, Germany), E. K. U. Gross (Max Planck Institute of Microstructure Physics, Germany), Miguel A. L. Marques (Martin-Luther Universität Halle-Wittenberg, Germany), and Christian Schilling (University of Oxford, United Kingdom).
Sponsors: CECAM, Psi-k and Max Planck Institute of Microstructure Physics.
This international workshop discussed and explored new aspects and challenges in Reduced Density Matrix Functional Theory (RDMFT). The main aim was to bring together leading experts in the field to address and carefully discuss open challenges in RDMFT such as implementations of 1-particle symmetries, extensions to open-shell atoms and molecules, time-evolution, temperature dependency and new insights about RDMFT from recent progress on the 1- and 2-body N-representability problems and density matrix renormalization group. The list of speakers was carefully chosen to include experts in various disciplines required for the accomplishment of the proposed scientific program. To maximize the success of the workshop, we asked all speakers to provide rather informal and interactive presentations. We also asked them to share their slides and other supplemental materials with all the participants in advance, allowing them to prepare the workshop accordingly. This ‘homework’ enabled not only fruitful and stimulating scientific discussions, but also more involved questions.
Since electrons interact pairwise by Coulomb repulsion, the energies and other electronic properties of fermionic systems can be computed directly from the two-electron reduced density matrix (2-RDM), only. ”Banishing” this way the N-electron wave function with its exponentially many degrees of freedom, the entire quantum problem can be recast in the form of a very simple linear functional on the 2-RDM. However, the description of the 2-electron picture involves highly nontrivial representability conditions, and new approaches of the reduced electron pictures deserve to be explored. The most successful one so far is Density Functional Theory (DFT), an approach based on the Hohenberg-Kohn and Kohn-Sham theorems. Although DFT has seen a tremendous success in many-body physics, the search for highly accurate functionals has suffered from an intrinsic difficulty. Not only the exact functional for the exchange-correlation is unknown but also the one for the kinetic energy.
In 1975, Gilbert established in the form of ”Reduced Density Matrix Functional Theory” (RDMFT) a natural extension of DFT. RDMFT exploits the 1-electron picture by seeking a functional on the whole 1-electron reduced density matrix (1-RDM). Compared to DFT, the big advantage is that the kinetic energy can be described in an exact way. Any scientific effort can be solely spent on approximating the exchange-correlation functional. In contrast to the 2-electron picture, the representability conditions for the 1- RDM are known. While DFT resorts to a large zoo of engineered density-functionals, only about a dozen of 1-RDM-functionals have been proposed so far. Remarkably, those few and less developed functionals already allowed one to describe closed-shell systems with accuracies higher by one order of magnitude than DFT. Moreover, RDMFT has succeeded in predicting more accurate gaps of conventional semiconductors than DFT does and correctly captures the physics of the insulator-metal phase transition of transition metal oxides.
Yet, the theory has been hampered by the absence of a set of single particle equations. Unlike Kohn-Sham DFT or Hartree-Fock theory, RDMFT implies a set of coupled self-consistency conditions for the natural orbitals. Therefore, it is one of the big challenges in RDMFT to find ways to improve the efficiency of the current computational methods. Since the natural orbitals are known from the very beginning for translationally invariant 1-band lattice models, the condensed matter regime, in particular, and the concept of 1-electron symmetries, in general, are promising directions for the future.
So far, advances in 1-RDM and 2-RDM theory have been fostering the development of a plethora of new paradigms in theoretical physics. Those promise to promote unprecedented growth in our ability to explore computationally a vast number of chemical questions from condensed matter and quantum chemistry to (static and dynamic) electronic correlations and entanglement.
This international interactive workshop discussed and explored new aspects and open challenges in RDMFT, such as:
(1) new insights about RDMFT from recent progress on the 1- and 2-body N-representability problems,
(2) new insights about RDMFT from finite uniform electron gases, random phase approximation, and exact systems,
(3) implementation of 1-particle symmetries and translational invariance,
(4) extension of RDMFT to open-shell molecules, finite temperatures, and time evolution,
(5) electronic correlations, entanglement, and recent developments on fermionic orbital optimization, and
(6) separation and quantification of dynamic and static electronic correlations.
The program included 20 talks, given by the invited speakers, and 5 contributed talks, by young scientists. In the mornings the invited presentations were 75 minutes long (including 30 minutes for questions and discussions). In the afternoons they were 60 minutes long (with 15 minutes for questions and discussions). This way, the speakers had the time to give generous and interactive introductions, addressed to non-specialists, and also deep discussions to a more specialized audience. The contributed talks last 25 minutes.
The program started on Tuesday with a short introduction, given by two of the organizers. Carlos L. Benavides-Riveros and Christian Schilling introduced the scope and the expected methodology of the workshop. Above all, they encouraged the participants to participate actively in the scientific discussions. In the first session, Peter Gill (Australian National University) discussed the mathematical treatment of finite uniform electron gases and showed in which way they are a source of information for the construction and testing of new RDMFT models. Kasia Pernal (Technical University of Lodz) pointed out a couple of novel approaches to constructing new functionals within the framework of random phase approximation (RPA). Kasia gave a short introduction to the derivation of the MacLachlan and Ball expression and RPA functionals in DFT; afterward, she explained how to exploit this theoretical framework within RDMFT.
In the second session of Tuesday, there were presented new ideas and new applications of reduced density matrices. Andreas Savin (University Pierre and Marie Curie) argued that combining wave function methods with density functionals can be seen from a reduced density matrix perspective. In a joint work with Nektarios Lathiotakis, Nikitas Gidopoulos (Durham University) exhibited an approach to determine effective potentials for RDMFT. Jamal Berakdar (MLU Halle-Wittenberg) discussed applications of reduced densities for studying the thermodynamic behavior of nanoscale quantum structures (e.g. quantum spin systems with non-collinear magnetic order or quantum heat engines with a working substance being a helical multiferroic structure). Finally, Iris Theophilou (MPI for Structure and Dynamics of Matter) showed a mapping to a non-interacting system to solve the Hubbard model within RDMFT. Tuesday sessions ended with the poster session. Seven PhD students and postdocs from Poland, Germany, India, Japan, Iran, and Czechia presented their research results in the main hall of CECAM-HQ.
In the first session of Wednesday, we discussed the importance of 2-body representability conditions for constructing functionals in RDMFT. In practical applications, the energy functional of the theory employs the exact energy functional for the 2-RDM. However, an approximate expression for the 2-RDM is built from the natural occupation numbers and the natural orbitals of the 1-RDM. The so-called natural orbital functionals (NOF) are designed to satisfy some of the known 2-RDM representability conditions. Accordingly, in the first part of his talk, Mario Piris (University of the Basque Country) talked about the role of the N-representability in approximate 1-particle functional theories. In the second part, Mario presented a new method to achieve dynamic and static electronic correlations. Since in real computations one uses finite basis sets, in his talk Klass Giestbertz (Vrije Universiteit Amsterdam) pointed out some mathematical aspects concerning such a low dimensionality of the Hilbert spaces. He also discussed how crucial is a rigorous foundation of RDMFT.
In the afternoon, Pina Romaniello (University Paul Sabatier) stressed the relation of RDMFT with spectroscopy and provided some examples. Eduard Matito (Donostia International Physics Center) discussed how to separate dynamic and static electronic correlations using the relations between 2-RDM and 1-RDM. The expressions reached this way depend only on the natural occupation numbers. Peter Knowles (Cardiff University) exhibited an example of two wavefunctions with identical one-electron spectrum, but strongly different two-electron density matrices. To Peter, it means that algebraic density-matrix functionals cannot be exact. The question for the role of the generalized Pauli exclusion principle (with its constraints on the occupation numbers) in RDMFT was addressed by Nicole Helbig (Forschungszentrum Juelich).
On Thursday morning, Oleg Gritsenko (Vrije Universiteit Amsterdam) pointed out the crucial role of fractional occupation numbers in the description of double excitations obtained in time-dependent RDMFT. Nektarios Lathiotakis (Theoretical and Physical Chemistry Institute, Athens) started his talk with an overview of RDMFT and its main differences to DFT. Inspired by local DFT, Nektarios discussed the recent progress in developing effective Hamiltonians in RDMFT. In the afternoon, we had two talks on electronic correlations and tensor networks. Norbert Mauser (Wolfgang Pauli Institute) presented the so-called “nonfreeness”, the measure he and Alex Gottlieb introduced some years ago to quantify electronic correlations. A vivid discussion on how to quantify correlations in statistical mixtures followed. In his talk, Örs Legeza (Hungarian Academy of Sciences) overviewed tensor-network techniques and discussed how such techniques treat high-dimensional optimization tasks. No doubt, its versatility is one of the reasons why the theory is widely used in many-body quantum physics with long-range interactions and ab initio quantum chemistry.
We finished the day with the contributed-talk session. Our conference banquet was held at the restaurant Port de Pully, very close to Lake Geneva with —Lord Byron once wrote— its “stillness” and “stern delights”:
The conference finished on Friday with four talks. Sangeeta Sharma (MPI of Microstructure Physics) discussed her work in finding the correct ground-state properties of transition metal oxides (TMO). The good news is: RDMFT is able to capture the correct insulating state of TMO under ambient conditions. As well, away from ambient pressure, RDMFT correctly captures the physics of the insulator-metal phase transition. The bad news is that the minimization process in RDMFT must be upgraded in order to be used in infinite systems, for it is not fast enough to beat DFT or Hartree-Fock. Eugene de Prince (Florida State University) overviewed 2-RDM theory. The current variational 2-RDM approach can be used to realize polynomially-scaling complete active space self-consistent field. Paul Ayers (McMaster University) displayed some recent techniques to refine non-representable RDM. The workshop finished with the talk of Joshua Hollett (University of Winnipeg). Joshua stressed the importance of taking different approaches to electron correlations. He also discussed recent progress in deriving an “on-top” density functional for dynamic correlation. A closing word wrapped up our workshop.
Overall, this international conference was an interesting and stimulating meeting of scientists working in different areas of physics and chemistry connected with or inspired by reduced density matrices. It was, by and large, a great opportunity to discuss and point out new challenges for RDMFT. We hope this meeting will prompt the community to pursue new collaborations, boosting the versatility, development, and applications of RDMFT.
Some of the participants mentioned the possibility of another such meeting in two or so years, and we strongly hope that it can be repeated in the near future. Last but not least, we acknowledge the warm atmosphere and kind support of CECAM, Psi-k and Max Planck Institute of Microstructure Physics (Halle, Germany).
The workshop program, the abstracts of the talks and the posters, the PDF files with the slides used during the oral presentations, and some supplemental materials can be found on the official workshop’s webpage: https://www.cecam.org/workshop-1448.html.
Location: Abdus Salam International Centre for Theoretical Physics, Trieste (Italy), 3-7 July 2017
Organizers: David M. Ceperley (University of Illinois at Urbana-Champaign); Michele Ceriotti (Ecole Polytechnique Fédérale de Lausanne); Thomas E. Markland (Stanford University).
Local Organizers: Ali Hassanali (The Abdus Salam International Centre for Theoretical Physics); Sebastiano Pilati (University of Padova).
The main goal of this interdisciplinary workshop was to gather together physicists and chemists who employ computer-simulation methods based on path integrals to investigate different systems, ranging from chemical and biochemical compounds, to quantum fluids/solids, to ultracold gases. This event allowed a broad community of researchers to create a platform for exchanging knowledge and know-how on path-integral technology and on other approaches to the combined quantum simulation of electrons and nuclei. Furthermore, speakers had the opportunity to showcase the most recent applications to various intriguing quantum phenomena, including, e.g., isotope effects in aqueous systems, quantum fluctuations in enzyme catalysis, quantum phase transitions due to strong correlations, and tunnelling phenomena in molecular systems and in adiabatic quantum computers (alias quantum annealers), thus creating a new bridge between quantum chemistry and quantum computing.
This event took place at the ICTP Adriatico Guesthouse, in a warm and sunny Trieste, allowing participants to enjoy the view of the Adriatic sea and the Miramare park. The format included 24 (long) oral presentations given by invited speakers, 7 short talks selected from contributed abstracts, 21 flash presentations (meant to advertise the content of a poster), and a total of 24 poster presentations. The workshop was attended by a total of 80 participants (including directors and speakers) from 29 countries.
This event has been sponsored by ICTP and by the Psi-k Network.
Psi-k workshop on
“Atomic scale materials microscopy: theory meets experiment”
National Railway Museum, York (UK)
26-28 June 2017
Atomic scale materials characterization is now one of the major drivers of technological innovation in areas such as nanoelectronics, catalysis, medicine, clean energy generation and energy storage. This can in a large part be attributed to advances in electron and scanning probe microscopies, which are now able to provide atomically resolved structural, chemical and electronic characterization of a wide range of functional materials. However, the types of systems relevant to applications, which include surfaces, interfaces, nanocrystals and two-dimensional materials, are complex and interpreting experimental images and spectra is often extremely challenging. On the other hand, parallel advances in theoretical approaches means that theory can often offer invaluable guidance. These approaches include first principles methods for structure prediction, simulation of scanning probe and electron microscopy images, and prediction of various spectroscopic signatures (e.g. EELS and STS). Some of the most impressive examples of this kind of research in recent years have combined complementary theoretical and experimental approaches in a synergistic way to unravel the complex structure of materials. This type of integrated approach is increasingly being recognised as critical to advanced materials research and development by both industry and research funders.
It was in this context that the Psi-k workshop: “Atomic scale materials microscopy: theory meets experiment” was held between the 26th and 28th of June 2017 at the National Railway Museum in York (UK). The scientific focus was on the application and development of first principles methods that, in synergy with advanced microscopy techniques (e.g. TEM, EELS, STM, AFM), can help to unravel the structure and properties of materials at the atomic scale. Open to both experts and newcomers the aim was to provide a rounded overview of emerging methods and challenges in the field, and provide an opportunity for in-depth discussion and exchange of ideas. Continue reading SCIENTIFIC REPORT ON THE PSI-K WORKSHOP: “ATOMIC SCALE MATERIALS MICROSCOPY: THEORY MEETS EXPERIMENT”→
Organizers: Thomas Frauenheim (University of Bremen)
Qiang Cui (University of Wisconsin, Madison, USA)
Bob Hamers, University of Wisconsin, Madison, USA)
Joel Pedersen, University of Wisconsin, Madison, USA)
Location: University of Bremen, Germany,
12th June until 16th June 2017
The workshop “Tackling Complexity of the Nano/Bio Interface – Computational and Experimental Approaches” was held at the University of Bremen, Germany from June 12th to 16th 2017. In total, 72 participants from Belgium, Brazil, Finland, Ireland, Luxemburg, The Netherlands, Portugal, Slovenia, Spain, Sweden, Switzerland, Russia, France, Germany, UK and US attended the workshop.
In 2017, the ETSF Young Researchers’ Meeting made its way to Tarragona, Spain for the first time. Sunny weather, great food, a beautiful old city and the kind hosts at the Catalan Institute for Chemical Research (ICIQ) provided a fantastic setting for a week of science that will stay in our memory.
The Young Researchers’ Meeting (YRM) of the European Theoretical Spectroscopy Facility (ETSF) is a workshop organised by young researchers for young researchers. Every year, postdocs, PhD students and Master students gather from all over Europe to discuss problems and recent advances in theoretical and computational methods for the study of the electronic and optical properties of materials. The YRM is where you can present your work in progress, float new ideas, and learn from others at your own level – both scientifically and personally. Talks at the YRM are 25 minutes, which gives you enough time to introduce your topic, what you did and, crucially, how you did it. Each session starts with an introductory keynote that provides an overview of the field, introduces the theoretical framework and points out open questions. Continue reading 14th ETSF Young Researchers’ Meeting (Tarragona)→
18th Total Energy Workshop, ICTP, Trieste (Italy), 12-14 January 2017
The “Total Energy” Workshop is held traditionally in Trieste every two years, since 1987. It is devoted to recent advances in computational condensed matter physics and materials science, based on realistic calculations of the electronic structure of complex systems. It has become one of the most popular regular events of the international ab-initio electronic-structure community. The 2017 edition confirmed this tradition, with a large number of participants, lively discussions and, furthermore, with an impressive number of contributed posters. Overview, speakers list, program with the relevant material (Conference Book, abstracts, list of attendees, …) are available on the web page: http://indico.ictp.it/event/7948/overview
The Workshop involved 225 attendees, including Directors, Scientific Committee members, speakers, and selected participants.
Following the tradition of the previous meetings of the series, the Workshop has been structured in thematic sessions with oral presentations by invitation only. The aim was to gather speakers presenting current topics of research of broad interest as well as future research directions for the electronic structure community. The chairpersons introduced each session with a short overview (about 5 min) to set the subject and point out open problems. The introductions were very useful, especially for those people working on other subjects. In addition, large space was devoted to discussion. This format has been greatly appreciated and contributed to create, most noteworthy, a lively atmosphere.
Selected contributions from participants have been solicited as posters. The large number of selected posters (140) has been a testament of the enthusiastic and active participation of the attendees. Consequently, two large poster sessions have been organized.
Daresbury Laboratory was pleased to welcome 40 scientists to the “Questaal Hands-On Course” which took place over four days between May 16th and 19th. The Questaal software suite features the first all-electron GW code and the first implementation of the quasiparticle-self-consistent GW method, which is significantly more accurate and reliable than conventional density-functional methods. The focus of the course was to introduce these advanced methods to researchers already familiar with electronic structure calculations and to teach them the practical details needed to perform such calculations for materials and systems relevant to their individual research areas.
High-throughput computing (HTC) is emerging as an effective methodology in computational materials science for the discovery of novel materials and the optimisation of selected properties. Its adoption is spreading rapidly at the point that HTC is becoming an essential tool for computational materials scientists.
The aim of the tutorial was to introduce young researchers and more experienced practitioners to HTC, with hands-on tutorials based on the open-source high-throughput platform AiiDA (http://www.aiida.net), complemented by four invited keynote talks to overview the diverse application fields of HTC.