How many bonds are there in diatomic carbon (C2)?

Question: How many bonds are there in diatomic carbon (C2)? Answer: Who cares? It's a waste of time! Well, in the last ten years, there are debates about the "nature" of C2 chemical bond, leading to a bunch of papers in high-impact journals. A group of people claim that there are four bonds. Some say there are… Continue reading How many bonds are there in diatomic carbon (C2)?

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Paper review: pancake-bonded p-dimers: dispersion is not enough

A new challenge for DFT: pancake bond. In a nut-shell: The pancake bond is an intermolecular interaction between pi-radicals. Pancake bonding can be considered as a combination of van der Waals interaction and interaction between singly occupied molecular orbitals (SOMOs).   Kertesz et al. very recently showed that it's very difficult to describe the interaction… Continue reading Paper review: pancake-bonded p-dimers: dispersion is not enough

Watoc 2017, a negative review

Watoc 2017 is over, and I am exhausted. Tomorrow I have a long-haul flight back to my poor country. The conference is great, with many excellent talks. The organization is "German style": exact and efficient. There are several talks I'm going to discuss in this post, not because they are excellent, but because they raise… Continue reading Watoc 2017, a negative review

Playing with HF exchange in DFT

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

B3LYP* functional

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

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

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)