Questions tagged [ab-initio-calculations]

For questions about ab-initio (first principle) calculations.

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How ductile is C60? [closed]

According to a web page I can no longer find, some brittle materials such as glass have a very high theoretical strength but they tend to have surface cracks which magnify tension at the tip greatly ...
Timothy's user avatar
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13 votes
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A CCSD(T) geometry optimization in Gaussian09 is deviating too far from the minimum. How do I deal with it?

I am doing a CCSD(T) geometry optimization on a series of molecules. One of the geometry optimizations took about 2 weeks even though an analogous molecule with the same number of basis functions took ...
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Was Walter Kohn wrong about this?

In Kohn's Nobel Lecture, he claimed that: "In general the many-electron wave function $\Psi(\mathbf{r}_1,\ldots,\mathbf{r}_N)$ for a system of $N$ electrons is not a legitimate scientific concept,...
ProfM's user avatar
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Is there an example where TD-DFT fails to provide sufficient accuracy for a small system, where RI-CC2 is sufficient?

Time-dependent density functional theory (TD-DFT) is considered to be more efficient (in terms of its accuracy/speed ratio) than alternatives such as the approximate coupled-cluster singles and ...
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How accurately are magnetic effects treated in *ab initio* methods?

I am a condensed matter theorist and I mostly use quantum Monte Carlo methods. I use models like the Heisenberg model, an represent an extreme simplification of real materials to just localized spin ...
taciteloquence's user avatar
14 votes
2 answers
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How to calculate energy of a molecule in an aligned electric field?

So I am aware that many quantum chemical codes are able to add external fields to molecular calculations (for example to calculate polarizabilities). I also know that in some (eg. Orca) you have some ...
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23 votes
1 answer
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Which basis set families were optimized to give the lowest possible variational energy for a given number of orbitals?

Dunning's basis set families (such as cc-pVXZ and aug-cc-pCVXZ) were not optimized to give the lowest variational energy for a given number of orbitals. For example the S-type orbitals are optimized, ...
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14 votes
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Generating interatomic potentials via force matching [closed]

I am trying to learn best practices for force matching ab initio molecular dynamics (AIMD) data with nonlinear least-squares minimization to generate interatomic potentials for use in classical MD. I ...
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11 votes
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When running DFT on Q-Chem with an HPC cluster, why is parallelization with OpenMP faster than with MPI?

How to maximize the efficiency/time-to-solution of the calculations in Q-Chem on HPC clusters? MPI parallelization is supposed to improve time-to-solution as compared to OpenMP. The system I tested ...
Dmitry Eremin's user avatar
16 votes
1 answer
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Are there any ab intio/DFT methods to simulate solubility?

When designing molecules or materials (as drug carriers) in drug design, one important properties is the system solubility. Are there any software that using ab intio/DFT methods can be used to ...
Camps's user avatar
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Can DFT be considered an ab initio method?

Note added afterwards: This question also has excellent answers on the Chemistry Stack Exchange: Is density functional theory an ab initio method? I have very little experience with DFT, but coming ...
Prateek Goel's user avatar
17 votes
2 answers
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Can ab initio crystal structure methods predict the structure of cuprates from their stoichiometry and quantify the brittleness of those materials?

Current ab initio methods may not be able to predict the electronic transport properties of cuprate superconductors but can they be used to predict their crystal structure? Furthermore those materials ...
pldd86's user avatar
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12 votes
1 answer
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What limits the accuracy of ab initio methods in predicting the transition temperature of conventional superconductors?

Here I assume that conventional superconductors refer to materials that undergo a superconducting transition at low temperature as described by the Bardeen-Cooper-Schrieffer theory (BCS). For those ...
pldd86's user avatar
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26 votes
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What is the largest material that has been studied using density functional theory?

Quantum-chemical calculations are quite expensive with a cost that scales greatly with the number of atoms in the system. What is the largest material that has been modeled using density functional ...
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35 votes
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What are the positives and negatives of periodic DFT codes that don't use plane-wave basis sets?

Most periodic density functional theory (DFT) codes use plane-wave basis sets in conjunction with three-dimensional periodic boundary conditions. In contrast, for molecular systems of finite size, ...
Andrew Rosen's user avatar
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21 votes
1 answer
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What are some materials discovered from first-principles calculations that ended up being incorporated in a commercial product?

High-throughput computational screening, inverse materials design, and advances in machine learning have really accelerated the pace in which we can identify novel materials for a wide range of ...
Andrew Rosen's user avatar
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16 votes
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What methods can be used to calculate excited-states in molecular crystals?

In periodic systems plane-wave basis functions are often used. In a previous question on this site it was questioned if plane-wave basis-sets are reliable for modeling adsorption-processes The ...
Cody Aldaz's user avatar
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21 votes
3 answers
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Generating special quasirandom structures (SQS) for surface calculations?

Given that most of the available codes for performing DFT calculations work with periodic boundary conditions, there are tools like mcsqs as a part of the Alloy ...
Mythreyi's user avatar
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16 votes
1 answer
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k-points convergence for special quasirandom structures (SQS) of the same material containing different # of atoms

For an ordered crystal, we generally converge the k-mesh resolution for a primitive cell or other smaller supercells. We then use this resolution for any other size of the supercell for the same ...
Hitanshu Sachania's user avatar
25 votes
2 answers
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How to overcome the exponential wall encountered in full configurational interaction methods?

Similar to how a molecular orbital, also known as a 1-electron wavefunction, can be represented with a linear combination of “basis” functions, e.g., atomic orbitals (LCAO): $$\Phi(\mathbf{r})=\sum_i^...
Cody Aldaz's user avatar
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20 votes
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When using the "even tempered method" for augmenting basis sets, what justification is there for the numerical factor which is used?

Diffuse functions are often added to basis sets using "even-tempered" exponents, or sometimes I have heard the phrase "even tempering". In this paper by Jacek Koput, the author says "the customary ...
I have no free time anymore's user avatar
54 votes
5 answers
2k views

What is the closest thing we have to "the" universal density functional?

It is understood that finding "the" universal functional is an NP-complete problem. However, progressively better functionals have been constructed decade after decade and fitted to more and more ...
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57 votes
7 answers
2k views

Is there a database where we can find previously determined geometries of materials?

For small molecules, NIST has a database of experimentally determined geometries here, and ab initio geometries here. I wonder if there is something similar for materials?
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