Density functional theory: Wisdom of the crowd – GGA functionals

In the previous post, I used a bunch of LDA functionals to study the hydrogen bond in the water dimer. The idea is quite simple but unique and "novel": combine different exchange and correlation functionals and take an average result. In this post, I update the result with nearly 4000 GGA functionals. Let's discuss A… Continue reading Density functional theory: Wisdom of the crowd – GGA functionals

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Density functional theory: Wisdom of the crowd

Have you ever wondered if it is possible to use many different DFT functionals in your paper, not 5, not 10, or 20? I mean more than 100, or more than 1000? Can we use the results and estimate an average number as well as the standard deviation? In this post, I show that this… Continue reading Density functional theory: Wisdom of the crowd

Minnesota MN15 functional (and the others) – new challenge

As an attention seeker, I want to have more and more views for my blog. And you know what, the number of views of the MN15 posts (or DFT in general) is way higher than the other WFT posts. So today, I write (again) on MN15 and the other modern functionals. Of course, I will… Continue reading Minnesota MN15 functional (and the others) – new challenge

Adopting a new baby – v2RDM-CASSCF

In the previous post, I plan to use some "novel" multireference methods that can treat huge active spaces (up to 50 active orbitals). I now decide to adopt the first baby:  the variational two-electron reduced-density-matrix (2-RDM)-driven complete active space self consistent field (v2RDM-CASSCF). Why? Because Fun fact: in the paper, DePrince wrote “the chemistry community has… Continue reading Adopting a new baby – v2RDM-CASSCF

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)

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