Multireference methods – a review (part 1)

Over the years, developing or benchmarking DFT functionals has been a hot topic, for example D. Truhlar paper on M06 has reached over 9000 citations, or this paper of D. Jacquemin on (just!) TD-DFT benchmark of organic molecules receives more than 500 citations. This leads to a zoo of DFT functionals, and it's growing wild like weed.… Continue reading Multireference methods – a review (part 1)

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DFT: mid-life crisis

Doing DFT is fun: it's fast, easy, black-box, and you never know if your numbers are "predictive". Sometime your favorite functional works, sometime it fails miserably (and you hide the results). Deal with it! In this post, I'm not going to present any calculations. I want to propose my new TV show! Now DFT is… Continue reading DFT: mid-life crisis

Should we really worry about anharmonicity?

My colleague, Dr. Matas, asked herself a question. For a very shallow minimum on the potential energy surface (PES), is the quantum harmonic oscillator approximation (or rigid-rotor-harmonic-oscillator (RRHO)) still valid? Should we worry about its error, especially when calculating the entropy and free energy, which is extremely sensitive with respect to very small vibrational frequencies? The… Continue reading Should we really worry about anharmonicity?

Minnesota MN15 functional (and the others) – magnetic coupling constant – a benchmark study

Honestly, I don't like studying magnetic systems, e.g. single molecule magnet, and I don't know why I end up testing my three favorite functionals with this toy model H-He-H. You may laugh at this system but there has been at least 6 papers (six!, including one from Gustavo E. Scuseria) used this system as a model… Continue reading Minnesota MN15 functional (and the others) – magnetic coupling constant – a benchmark study

Minnesota MN15 functional (and the others) – SIE!

One of the main "feature" of Kohn-Sham DFT (KS-DFT) is the approximation of the exact exchange-correlation functional, leading to a zoo of functionals with many flaws. One such flaw is the self-interaction error (SIE), i.e. an electron can interact with itself! Reducing SIE is one of the goal when "designing" a new modern functional (by… Continue reading Minnesota MN15 functional (and the others) – SIE!

Minnesota MN15 functional (and the others) – part 3

It's sunny today, so I decided to perform just a small test (and spend the rest of my day staying outside) again with MN15, SCAN0, and ωB97M-V. The molecule is small, Fe(CO)4, inspired from the work of Harvey et al. (here and here). In these works, the authors studied the singlet-triplet gap ΔE = E(LS)… Continue reading Minnesota MN15 functional (and the others) – part 3

Minnesota MN15 functional (and the others) – an update

Thanks to the author of Erkale: The bug with SCAN0 is fixed. My calculation with Erkale is now faster. I should have included the computational details with Erkale: e.g. DFTGrid(75,302), or default Cholesky decomposition for the two-electron integrals (produce an error of ~1 kcal/mol). So here, this is a small update of my previous post (remember I… Continue reading Minnesota MN15 functional (and the others) – an update

Symmetry, or not symmetry, that is the question

Let's try to answer a question. How faster a calculation can be by exploiting molecular symmetry? Suppose we want to do a CCSD(T) calculation of benzene C6H6. The symmetry point group is D6h but for correlated methods, we can only employ at most D2h (the highest Abelian group). Then, how will the calculation be slower… Continue reading Symmetry, or not symmetry, that is the question

Minnesota MN15 functional (and the others)

See a small update here. Last year I was at the 8th MQM conference and attended a talk of D. Truhlar advertising his latest Minnesota functional, the MN15 functional. According to his talk, this functional is good at describing everything, including multireference problems. I was quite skeptical of that. Last week, one of my colleagues… Continue reading Minnesota MN15 functional (and the others)