THE EVANGELISTA LAB

A 2007 review of coupled cluster theory by Bartlett and Musial (Bartlett, R. J.; Musiał, M. Coupled-Cluster Theory in Quantum Chemistry. Rev. Mod. Phys. 2007, 79, 291–352) opens with an intriguing quotation of a 1989 article by physics Nobel prize winner Kenneth Wilson:

Ab initio quantum chemistry is an emerging computational area that is fifty years ahead of lattice gauge theory…and a rich source of new ideas and new approaches to the computation of many fermion systems.

I recently read this paper (Wilson, K. G. Ab Initio Quantum Chemistry: a Source of Ideas for Lattice Gauge Theorists. Nuclear Physics B – Proc. Suppl. 1990, 17, 82–92) and found it extremely interesting. The article begins by saying that Wilsons had switched his field of research from lattice gauge theory to computational quantum chemistry. One of the reasons for this change, Wilson says, is ancestral, adding an interesting explanatory note in which he acknowledges discussions with his father, E. B. Wilson. The second reason he reports is the lack of sources of inspiration in his field.
In his paper Wilson discusses the benefits of using Gaussian basis functions compared to numerical grids, the emphasis of quantum chemistry on analytic approaches rather than stochastic methods, and “the status of my efforts to ease the programming burden using the C++ programming language”.
In just a few pages, Wilson summarizes with extreme clarity the state-of-the-art in quantum chemistry (in 1989). He provides a very clear description of the major challenges in this field, and succinctly analyzes purpose and limitations of some of the most important methods used in quantum chemistry.

To my surprise, Wilson was at the time also concerned with the software productivity of scientists, an issue that is still very relevant today. I was quite excited to see that Wilson had already recognized the potential of C++ to simply the organization of large computer codes. In Wilsons words:

The ability to attach variable names and subroutines and functions to a common block is, I find, a powerful organizing
tool for large programs.

I think this article is a little gem and recommend it especially to those interested in the history of physics and quantum chemistry. I hope you will enjoy reading it!

Last week we had our first group hackaton to develop our quantum chemistry code FORTE.  During our first session we established a new git repository and revised test cases.

Here is a photo of Jeff receiving the prize for his poster presented at SETCA 2015, University of Central Florida,  Orlando.

• Tensor product methods and entanglement optimization for ab initio quantum chemistry. This review of tensor product approximations in quantum chemistry by Szalay et al. was just posted on arXiv. At times a bit formal, this is a nice introduction to the topic.
• In Search of a Rational Dressing of Intermediate Effective Hamiltonians. This is a paper on intermediate Hamiltonian theory, an approach to deal with the intruder state problem in effective Hamiltonian theories. From the abstract: The intermediate effective Hamiltonians are designed to provide M exact energies and the components of the corresponding eigenvectors in the N-dimensional model space, with N > M. The effective Hamiltonian is not entirely defined by these N × M conditions, and several dressings of the Hamiltonian matrix in the model space are possible.
• Appointing silver and bronze standards for noncovalent interactions: A comparison of spin-component-scaled (SCS), explicitly correlated (F12), and specialized wavefunction approaches. A systematic investigation of the accuracy of non-covalent interaction predicted with various quantum chemical methods by Burns and co-workers. From the abstract: After examination of both accuracy and performance for 394 model chemistries, SCS(MI)-MP2/cc-pVQZ can be recommended for general use, having good accuracy at low cost and no ill-effects such as imbalance between hydrogen-bonding and dispersion-dominated systems or non-parallelity across dissociation curves. Moreover, when benchmarking accuracy is desirable but gold-standard computations are unaffordable, this work recommends silver-standard [DW-CCSD(T**)-F12/aug-cc-pVDZ] and bronze-standard [MP2C-F12/aug-cc-pVDZ] model chemistries, which support accuracies of 0.05 and 0.16 kcal/mol and efficiencies of 97.3 and 5.5 h for adenine·thymine, respectively.