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29 votes
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How accurate are the most accurate calculations?

Exhibit 1: Ground state hyperfine splitting of the H atom: ...
Nike Dattani - No Free Time's user avatar
26 votes
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Why is the band structure of a supercell more dense than for simple cell?

What you are referring to is called band folding. Remember we are plotting the band structure in the reciprocal space. As the size of the cell in real space increases (eg: when you make a super ...
Thomas's user avatar
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18 votes
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How to do periodic DFT calculations using Quantum ESPRESSO?

Unlike non-periodical DFT codes, Quantum ESPRESSO uses planewave basis sets and pseudopotentials. There are many ways of writing your input file, and it all depends on what information you have or ...
epalos's user avatar
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18 votes
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How are charge transfer processes modeled in materials?

Here is a paper reviewing charge transport in molecular junctions: J. Chem. Phys. 148, 030901 (2018), http://dx.doi.org/10.1063/1.5003306 A typical way to treat such a problem is to couple the Non-...
Fabian's user avatar
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17 votes

When do I use the lattice parameters obtained computationally vs experimentally?

To respond directly regarding the Materials Project data, I'm a staff member there so maybe I can shed some light. Materials Project computed data is currently generated using a technique known as ...
Matt Horton's user avatar
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17 votes
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What are the positives and negatives of periodic DFT codes that don't use plane-wave basis sets?

Pure plane-wave basis sets have the following advantages when used in periodic DFT (or HF) simulations: Orthogonal Computationally simple (operators with derivatives are particularly straightforward) ...
Phil Hasnip's user avatar
  • 8,142
17 votes

What are the positives and negatives of periodic DFT codes that don't use plane-wave basis sets?

The main positives: you can do all-electron calculations you don't need to set up pseudopotentials / PAWs you can study core properties you can use hybrid functionals cheaper / run post-HF ...
Susi Lehtola's user avatar
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14 votes

What are the positives and negatives of periodic DFT codes that don't use plane-wave basis sets?

One important property of atom-centered basis sets is that electrons can only be localized on atoms. This is a problematic property when modeling solid systems with defects. For instance, at a color ...
Franziska Heß's user avatar
14 votes

How to do periodic DFT calculations using Quantum ESPRESSO?

You can start with following this Quantum Espresso Tutorial. The tutorial includes Hands On: scf, Energy bands, eqn of state, Geometry, cell optimization, Magnetism, DFT + U, CPMD, TDDFT, GW, Phonos, ...
Thomas's user avatar
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13 votes

Moving from VASP to CASTEP for bulk crystal and surface calculations

As the answer above mentioned, the biggest difference is perhaps CASTEP takes two input files with suffix "cell" and "param", other things are very similar. After all, both ...
bzbzbz's user avatar
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12 votes

How to do periodic DFT calculations using Quantum ESPRESSO?

Regarding input file format, check this website: https://www.materialscloud.org/work/tools/qeinputgenerator Format from this website will provide you a starting point. But please remind that the ...
exsonic01's user avatar
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12 votes

What is the status of graphics processing units in plane-wave DFT?

I can't say much about the popularity of GPUs in practical calculations. From a development point of view the speedups that can be expected from GPUs in plane-wave DFT are only moderate, probably ...
Michael F. Herbst's user avatar
12 votes
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Moving from VASP to CASTEP for bulk crystal and surface calculations

The workflow transferring from VASP to CASTEP is quite similar. Within VASP, there are four main files that you need for a calculation: POSCAR – gives the positions of the atoms within the unit cell ...
benshi97's user avatar
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10 votes

When do I use the lattice parameters obtained computationally vs experimentally?

I will give a quick answer from my experience, but typically you want to use the computed lattice parameter. The reason for this is that otherwise you induce strain in your computed cell, but in ...
Tristan Maxson's user avatar
10 votes

What is the status of graphics processing units in plane-wave DFT?

While I can't comment on concrete speed-ups as I'm not very familiar with GPU programming itself, I would like to point out that most of the computing time is spent in FFT and GEMM (matrix matrix ...
Fuzzy's user avatar
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9 votes

What is the status of graphics processing units in plane-wave DFT?

I experienced[1] about 5-10 times speedup with GPU accelerated Quantum Espresso on Tesla V100 32 Gb compared with Intel Core i7 9700K processor with 8 cores and 32 Gb RAM. The above mentioned system's ...
user36313's user avatar
  • 730
8 votes

How are charge transfer processes modeled in materials?

Here's another approach for strongly correlated systems: Al-Hassanieh et al. Phys. Rev. B 73 195304 2006. In this case, they use time-dependent DMRG. They treat the wire as a chain of sites occupied ...
taciteloquence's user avatar
8 votes

When do I use the lattice parameters obtained computationally vs experimentally?

I have to disagree with the answer of @Tristan. The x-ray diffraction, both powder and single crystal, has enough precision and quality (equipment and software) to give very good and real experimental ...
Camps's user avatar
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8 votes

Is there any Python library for returning the atoms of a periodic material within a cube?

You can use a python library called ASE (Atomic Simulation Environment) to achieve your requirement. Here is a sample code: ...
Vandan Revanur's user avatar
8 votes
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Pattern X-Ray Diffraction Fitting

You have two different question in the same post. how can I simulate the powder XRD spectra? To just simulate the XRD spectra you can use this answer https://mattermodeling.stackexchange.com/a/146/...
Camps's user avatar
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8 votes
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Guess cell parameters from atomic coordinates

It is possible to approximate the cell parameters by determining the convex hull of the molecule and then computing the smallest parallelepiped that encloses it. This will automatically give the ...
TheSimpliFire's user avatar
6 votes

Unit Cell Parameters for VASP Calculations

There some very important points to address here. In a periodical structure, the atom coordinates and the cell parameters are not randomly selected. The crystal structure (atom positions, cell ...
Camps's user avatar
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6 votes
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Why use PySCF/OpenMolcas instead of VASP/QuantumESPRESSO

The main difference is that PySCF, OpenMolcas, and other popular software such as Gaussian, ORCA, Molpro, Psi4, MRCC, CFOUR, Dalton, GAMESS, COLUMBUS, ACES, etc., are very well-developed for using ...
Nike Dattani - No Free Time's user avatar
6 votes
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what determines the 'Estimated total dynamical RAM ' in a Quantum Espresso calculation

When people talk about the scaling of a conventional DFT implementation being cubic with simulation size, they are talking about the computational time, not the RAM required. The RAM actually scales ...
Phil Hasnip's user avatar
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5 votes
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What is the status of graphics processing units in plane-wave DFT?

I recently installed VASP GPU version provided by NVIDIA (here's the installation tutorial) on my machine that has an RTX 2080 Ti GPU. GPU version was announced for ...
Achintha Ihalage's user avatar
5 votes
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Transition dipole matrix element

Expanding my comment to an answer, I believe the "trick" is incorrect. As far as I'm aware, the relationship between $\boldsymbol{r}$ and $\boldsymbol{\nabla_k}$ is $$\boldsymbol{r}\to-i\exp(...
5 votes
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What is the difference between a "periodic image" and a "nearest image" in MD simulation?

You can generate a periodic image n times in any direction. In comparison, the nearest image is the one that is calculated as +x or -x in the x-direction, +y or -y in the y-direction and +z or -z in ...
Hemanth Haridas's user avatar
5 votes
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Screened Coulomb interaction and its direct Fourier transform

The following is not mathematical rigorous. Most importantly, I want to stress that it is hard to make precise statements without knowing the conventions and definitions of the source (which doesn't ...
Jakob's user avatar
  • 757
4 votes

What is the difference between a "periodic image" and a "nearest image" in MD simulation?

In the general case, we have lattice vectors ${\bf L}_{i}$, which may not be orthogonal. With periodic boundary condition, a particle at ${\bf r}$ has periodic images at ${\bf r}+n_1{\bf L}_1+n_2{\bf ...
Susi Lehtola's user avatar
  • 19.8k
4 votes
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Plane-wave basis expansion for periodic material modelling: cutoff energy inequality and number of atoms in the simulation

You’re quite right: as written, the equation is dimensionally inconsistent. There are actually a bunch of constants that make the units work out, but it is customary in matter modeling to define units ...
elutionary's user avatar
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