*From*: Susi Lehtola <susi.lehtola-x-alumni.helsinki.fi>*Subject*: CCL:G: All electron basis set for H2Te*Date*: Mon, 21 Jan 2019 19:57:18 +0200

Sent to CCL by: Susi Lehtola [susi.lehtola%x%alumni.helsinki.fi] On 1/21/19 2:27 PM, Mo Fateh mo.fateh+/-yahoo.com wrote:

Sent to CCL by: "Mo Fateh" [mo.fateh]_[yahoo.com] Dear CCL Subscribers, I am going to do geometry optimization for H2O, H2S, H2Se, and H2Te using Gaussian 09. What is the suitable All electron basis set for optimization with B3LYP? I have checked the Gaussian website and found that the following bais sets are suitable: 1- DGDZVP basis set 2- QZVPand Def2 3- UGBS basis set Which is one you recommended? and Why? Please suggest any other suitable basis set

First, do you really need an all-electron treatment? Using an effective core potential (ECP) typically gives you good results with a low cost. The def2 sets are not all-electron, but use relativistic core potentials starting from the 5th period. In addition to def2, you can also use the correlation consistent series, cc-pVXZ-PP, for the heavy atoms, which employs ECPs. These are probably not in the code you are using, but you can download the sets from the Basis Set Exchange (BSE) at https://bse.pnl.gov/bse/portal. If you want to do all-electron calculations, then you have to include relativistic effects to get any kind of reasonable accuracy. It looks like Gaussian can do second-order Douglas-Kroll-Hess (DKH2) calculations, and that the program uses a finite nuclear model in such a case. But, when you do a relativistic calculation, you have to make sure that the basis set has actually been designed for the method you are using. Unfortunately, there aren't many relativistic basis sets available on BSE. IIRC, the ANO-RCC set by Almlöf, Roos, and coworkers available on BSE has been parametrized with DKH2, so that would be an okay choice. Then, there are the x2c-SV(P)all, x2c-SVPall, x2c-TZVPall and x2c-TZVPPall basis sets by Pollak and Weigend, which are all-electron versions of the def2 basis sets; however, these basis sets have been formed with the eponymous X2C approach which differs from DKH2, and so the contractions may not be right for DKH2. If you want to play on the safe side, you could decontract these sets; like I implied before, the main problem with different relativistic models is that the core orbitals may be dissimilar. Using a fully uncontracted basis set takes away this problem; of course, then your basis set becomes larger. Personally, I would recommend either using ECP sets like def2, or if you really need all electrons, then I'd go with the x2c series. These are both commonly used, so I'd expect fewer problems. UGBS is a fine basis set for mean-field calculations on atoms. The problem is just that it is pretty huge (71, 84, 163, and 179 for O, S, Se, and Te, respectively), while it lacks polarization and correlation functions altogether. This means that calculations in molecules and/or at a post-HF level of theory will be unbalanced; you could trade off a small decrease in accuracy for atoms for a large improvement for molecules with the same number of basis functions by using a different kind of basis set. There are variants of UGBS with polarization functions, but 1) these are much larger than even the plain UGBS basis set; several hundred functions per atom, 2) I haven't been able to find any description on how the polarized basis sets have been formed, and 3) I am not aware of any accuracy benchmarks with these sets. -- ------------------------------------------------------------------ Mr. Susi Lehtola, PhD Junior Fellow, Adjunct Professor susi.lehtola-*-alumni.helsinki.fi University of Helsinki http://susilehtola.github.io/ Finland ------------------------------------------------------------------ Susi Lehtola, dosentti, FT tutkijatohtori susi.lehtola-*-alumni.helsinki.fi Helsingin yliopisto http://susilehtola.github.io/ ------------------------------------------------------------------