Let me get this straight, it's a very bad idea to change the HF exchange in a functional, just in order to fit your expectation or the experimental results. But today, I'm going to do this horrible thing. The reason comes from this Watoc abstract from Burke et al. Basically, the authors claimed that For Fe(II)… Continue reading Playing with HF exchange in DFT
Nowadays, reproducing results from a paper is extremely difficult: There are too many methods, too many software with different implementation. Sometimes we can find "wrong" information from the manual or "experienced" users. Computational details are poorly described, sometimes they are hidden by the authors. Today, I will show you an example with the B3LYP* functional.… Continue reading B3LYP* functional
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
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
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
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)
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
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?
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
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!