# Tag Info

8

Susi is right that these are called double hybrids, I'll just add a bit more to complement that correct answer. My answer to "What are some recent developments in density functional theory?" was about double hybrids, and it looks like the community here considered that to be one of the most important "recent" developments in DFT. About ...

10

These are called double hybrid functionals. You add a fraction of MP2 correlation on top of the DFT energy. A good reference is e.g. the review by Goerigk and Grimme from 2014 published in WIREs 4, 576 (2014). Note that this is already 7 years old; many double hybrids have appeared since then. However, it should give you a good overview.

9

Yes, broken symmetry solutions do break time-reversal symmetry, and that's one of the reasons why they are unphysical when the total magnetic moment of the system is 0 (although they are physical when the total magnetic moment is not 0, due to spin polarization). The reason is that, suppose you have a spin polarized $M_S=0$ state, then if you flip the spin ...

8

Comparing what each software is capable off, is relative easy: open both webpages and look for feature pages. From SIESTA project page: Total and partial energies. Atomic forces. Stress tensor. Electric dipole moment. Atomic, orbital and bond populations (Mulliken). Electron density. Geometry relaxation, fixed or variable cell. Constant-temperature ...

5

If you want to use quantum chemical programs as packaged for and distributed by your Linux distribution of choice, the long term support (LTS) releases of the Ubuntu familiy are typically good to familiarize with the program in question, and to perform many types of computation. If you opt for a light-weight desktop environment (e.g., Xfce as in Xubuntu) ...

6

Another advantage of using Linux is that it's more portable if you later end up switching to supercomputing facilities. Most jobs I've been involved with have had just enough shell scripting etc. in there for things to go wrong if not tested on a sufficiently similar system. Running a long job is no fun if your script copied the wrong input file over, or (...

7

"Is Ubuntu a better option than Windows for DFT calculations?" The vast majority of quantum chemistry and solid-state physics software were designed/developed for Linux. Your comment says you're specifically interested in Quantum ESPRESSO, and we recently had someone else complain that Quantum ESPRESSO was not performing the way they expected when ...

6

Well, my advice is to always check benchmarks before doing any consideration. I suggest you to follow the phoronix website because here you can read a lot about Linux benchmark in terms of different distributions, different hardware and also some comparison with windows OS. For example here you can find performance benchmarks comparing Ubuntu and Ubuntu on ...

10

As previously commented, any Linux distro will be much better than Windows to run simulations. About your first question: Is Ubuntu a better option for DFT calculations? No, it is not. But there is nothing special about Ubuntu, any Linux distribution would be a better choice than Windows. You can use Ubuntu or other distros like Mint or the father of them, ...

5

The final equation you quoted merely serves to define $F_{XC}$, which is plotted in Fig. 1 of the article to succinctly illustrate the behavior of the PBE functional as a function of density and density gradient. Without removing the $\epsilon_X^{unif}(n)$ factor from $E_{XC}$, one cannot plot the $r_s=0$ and $r_s=\infty$ curves anymore, that's why the ...

4

Quantum confinement is a kind of physical effect, which describes the change of electronic and optical properties when the material sampled is of sufficiently small size----typically 10 nanometers or less. For layered TMDC materials, when the materials are downsized to the 2D limit, the dielectric screening environment will be reduced significantly, and ...

7

This is just the Gaussian cube format. It's essentially a voxel dump of the wave function evaluated on a grid. You can find some documentation at http://paulbourke.net/dataformats/cube/ and https://h5cube-spec.readthedocs.io/en/latest/cubeformat.html . Most electronic structure programs are able to generate Gaussian cube files. Several molecular viewers can ...

13

There was a bug with the PModel guess of iodine, which leads to a very poor initial guess for molecules containing iodine, and consequently divergent SCF calculation. This bug has been fixed in ORCA 5.0. ORCA 5.0 can be downloaded at https://orcaforum.kofo.mpg.de/app.php/dlext/?cat=13. Note that ORCA 5.0 does not support the keywords Grid5 and FinalGrid5 ...

9

The actual external potential of molecules is indeed a sum of the Coulomb potentials of the nuclei (except when one uses a pseudopotential, where the potential will be Gaussian-like near the nuclei; but pseudopotentials are approximations). The point is that, there is also a one-to-one correspondence between the sum of nuclear-centered Gaussians and the sum ...

6

Please read the pw.x documentation on the Bravais lattice index (ibrav). The cell vectors for the primitive cell corresponding to the cubic face-centered Bravais lattice (ibrav=2) are v1 = (a/2)(-1,0,1), v2 = (a/2)(0,1,1), v3 = (a/2)(-1,1,0) The cell volume is $V=|v_1 \times v_2 \cdot v_3| = (a/2)^32=328.85\ \mathrm{a.u.}^3$

3

I would just like to point out that the question explicitly mentions adsorbing atomic oxygen rather than $\mathrm{O_{2}}$ (without mentioning the oxygen source or the surface). One can therefore somewhat simplify the question to: what is the strongest bond the oxygen atom can form? In molecules, the strongest bond is the C≡O triple bond in carbon monoxide at ...

4

This question is a bit old now, but hopefully my answer can complement Thomas's for anyone who comes across it. While "materials" is not in the name of the book, I think great (though more advanced) introductions to these topics can be found in Thijssen's Computational Physics. What's nice about it is that it covers the theory, provides coding (as ...

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