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What are the practical limitations of R12/F12 methods?

Electron correlation methods based on an expansion of the $N$-electron wavefunction in terms of Slater determinants have a slow basis set convergence. Moreover, explicitly correlated methods (such as ...
5
votes
1answer
26 views

How much does the initial geometry effect the final geometry in optimization calculations?

This might be a stupid question but to what extent will the initial configuration of a bulk phase geometry optimization calculation effect the final geometry? Most places say to start with ...
5
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0answers
25 views

Materials Modeling with Raspberry Pi?

Does anyone have any knowledge or direction for creating a homemade Beowolf cluster for materials modeling? I would like to be able to run my own "hobby" simulations at home, so a low energy, low ...
6
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0answers
28 views

Running quantum espresso calculations in google colab

So one big problem I experience in doing calculations with quantum espresso is that many calculations require a lot of computing power: you need large RAM capacities and powerful processors especially ...
12
votes
1answer
179 views

Difference between Van der Waals (DFT-D and DFT-D3) corrections in ab-initio calculations

In Kohn-Sham DFT calculations, Van der Waals corrections are often implemented in the structure optimization calculations because the typical functionals such as LDA and GGA are found to not treat ...
9
votes
1answer
74 views

What is the mathematical condition that ensure that the self-consistent field (SCF) procedure must converge?

We know that there is convergence issue of DFT method on study real molecular system. It would be conducive if people could pre-determine if the SCF procedure is converge analytically before starting ...
3
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0answers
15 views

Can you model Radiation Chemistry with existing MD software?

I'm wondering if it is possible to simulate the chemical changes materials undergo when exposed to ionizing radiation for a finite period of time with Molecular Dynamics (MD) software. In principal ...
10
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2answers
265 views

How does the Hartree-Fock method improve on Hartree after considering the wavefunction that takes the anti-symmetry property into account?

I am not able to understand the math of this. After taking the Slater determinant as a wavefunction in Hartree-Fock, does the procedure to find wavefunctions remain the same as in the Hartree method ...
11
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1answer
40 views

How the projected density of states is built

I'm new to DFT. I'm trying to figure out how projected density of states (PDOS) is built in solid state physics software package. I understand the basics of the density functional theory method: each ...
9
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1answer
63 views

What is the impact of the orientation of a molecule in cartesian coordinates to molecular properties?

According to my knowledge, each computational chemistry code optimizes a molecule keeping the input orientation of the molecule. The population and spectral analysis is performed on the optimized ...
9
votes
1answer
110 views

Predicting linear dependencies in a basis set in advance of calculating any integrals

I've been doing some calculations for a water molecule, with a big uncontracted basis set: For oxygen I am using aug-cc-pV9Z supplemented with the "tight" functions from cc-pCV7Z. The s-type exponents ...
6
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0answers
18 views

Can we do anything to reduce the number of displacements in a frozen phonon lattice dynamics study?

I realize that the more ordered the supercell is, the lower the number of displacements. Perhaps, we could say the same with respect to symmetry. Is there anything that can be done to reduce the ...
6
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0answers
30 views

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 ...
11
votes
1answer
102 views

Since MKL is not optimized for AMD hardware, should I use a math library specific to AMD, or would an open-source one be just as good?

The codes for quantum mechanical calculations make heavy use of linear algebra, and it seems most of them delegate this task to time-tested and highly optimized libraries, instead of trying to deploy ...
7
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0answers
40 views

Discrete molecular models

It seems to be taken in Cheminformatics that molecules with similar physical structure tend to have similar chemical properties https://dl.acm.org/doi/pdf/10.1145/2366316.2366334 Based on this, our ...
7
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0answers
53 views

Is there any literature that systematically analyzes current quantum chemistry algorithms using Big O notation for time and memory cost?

Big O notation is commonly seen in the papers on novel computational methods. However, only a few of them include rigorous analysis of the algorithm. Is there any literature that summarizes current ...
6
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0answers
26 views

Avoiding charge-migration in electronic structure calculations with solvent like environments

When performing electronic structure calculations on a molecule one can surround it with point charges to mimic a solvent environment and lend polarization effects. There is a bit of caveat ...
6
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0answers
22 views

2D Brillouin zone generator

There are several pages where you can find scripts/simulations to generate the first Brillouin zone for square and hexagonal 2D lattices. I wonder if there is a tool to generate the Brillouin for ...
12
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1answer
229 views

Labeling of high symmetry points in Brillouin zone

A Brillouin zone is defined as a Wigner~Secitz primitive cell in the reciprocal lattice [1,2]. The construction of the first Brillouin zone for two different 2D lattices are shown below: The ...
8
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1answer
90 views

Is it possible to use the Parrinello-Rahman barostat for NPT simulations in CP2K?

It is possible to use different types of thermostats in CP2K by specifying them in the corresponding section of the input as mentioned here. But there is no mention of specifying the barostat type in ...
11
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0answers
59 views

How to optimize zinc oxide bulk structure at certain pressure with LAMPPS

** edited ** I am trying to simulate the Zinc oxide bulk structure (periodic) with many different pressures to observe phase changing. Initially I would like to achieve constant pressure at 0.0 bars ...
11
votes
1answer
60 views

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 ...
6
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0answers
25 views

Calculation of local dielectric constant from MD output?

Has anyone been able to successfully calculate a local dielectric constant profile from MD output positions and charges? All the papers I have found seem to focus on calculations for the entire system....
11
votes
1answer
232 views

Is there any software that is optimized specifically for QM/MM?

A lot of codes can do QM/MM, and I am not naively asking if there is a program that can do QM/MM. What I am interested in is a program that is purely QM/MM meaning that it is designed and optimized ...
12
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2answers
166 views

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 ...
21
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2answers
2k views

What are the “smart algorithms” applied in computational chemistry to solve the “curse of dimensionality” problem?

The "curse of dimensionality" is an ubiquitous issue arise in both electronic structure and quantum molecular dynamics in computational chemistry, which refers to the exponential scaling of the ...
13
votes
2answers
618 views

What exactly is the “Optimizer” in CP2K geometry optimization?

I'm just now starting to use the program CP2K, and I am having trouble understanding the difference between the optimizer options (CG, BFGS, LBFGS). I have seen ...
13
votes
1answer
114 views

CCSD(T) Transition State and Ground State Calculations in Gaussian09: “Unable to Determine Lambda”?

I’m doing CCSD(T) calculations (for both transition and ground state geometries) on a series of small molecules in Gaussian09. Several similar calculations terminated without any problems but one TS ...
12
votes
2answers
404 views

Is there a performance difference when using fractional coordinates instead of Cartesian coordinates?

In general, the CIF file with the crystal structure uses fractional coordinates for setting the atoms positions. In this type of coordinates, the atom positions are relative to the cell parameters. ...
13
votes
1answer
57 views

VASP Dielectric constants: What potential to use?

I've simulated the dielectric constants using the LEPSILON = .TRUE. tag and the PBE GPAW potentials. A collegue mentioned that for accurate results norm conserving pseudo-potentials are the way to go. ...
13
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0answers
64 views

Understanding the GTH Pseudopotential

I'm new to DFT. I want to make use of the GTH pseudopotential. I am trying to understand how this potential works. I read the article "Separable dual-space Gaussian pseudopotentials" by S. Goedecker, ...
14
votes
3answers
580 views

How to write my own density functional theory (DFT) code in Python?

I am a DFT user and at some point in the future, I would like to write my own DFT code in Python to help gain a deeper understanding of DFT. As mentioned in a previous answer people have written their ...
17
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2answers
1k views

How to “get my feet wet” in Density Functional Theory by simulating a water molecule using Python

I just saw I am a beginner in Density Functional Theory. What are some resources that could help me to learn the basics? and it reminded me that few years ago I'd asked How can I calculate the charge ...
13
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0answers
46 views

Hexagonal lattice volume EOS fit

I have a little problem concerning hexagonal volume fitting using VASP. I have followed these steps: Relax the structure from a given volume using ISIF =4 Copy ...
16
votes
3answers
724 views

I am a beginner in DFT. What are some resources that could help me to learn the basics?

I am a beginner in DFT. Please suggest me some good material to understand the basics.
12
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0answers
73 views

How to calculate homolytic bond dissociation energies?

An experimental colleague asked me how hard it would be to calculate homolytic bond-dissociation energies for different phosphonates which are involved in a Hydrophosphination. The compounds include ...
10
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2answers
122 views

Converting adsorption binding energy to absolute temperature

The binding interaction energy during the adsorption of system B on system A can give an idea if the interaction is favorable (negative value) or unfavorable (positive value). Also, the absolute value ...
6
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0answers
31 views

How to understand dynamical spin structure factor?

A newish area of interactions between quantum Monte Carlo (QMC) and experiments is in spin spectra. Recent improvements in stochastic analytic continuation have made it much easier to compare extract ...
15
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0answers
48 views

Cancellation of Errors in density functional approximations or any wavefunction based methods

I am curious to find references for when is it TRUE that the error cancellation in approximate methods like DFT/MP2/etc. are valid and when they fall apart. For example: My understanding is (please ...
10
votes
1answer
40 views

Parse linked frequency calculations with cclib

I have multiple Q-Chem output files for TS search starting and finishing with frequency calculations (two sets of calculated IR data in total). To parse and plot spectra I use cclib and a script ...
13
votes
0answers
40 views

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, ...
10
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0answers
36 views

Developing skill in force matching of interatomic potentials?

I am building skills in using force matching from AIMD data (nonlinear least-squares minimization) to generate interatomic potentials for use in classical MD. I understand the concepts of selecting ...
4
votes
1answer
148 views

How is the material $\ce{\alpha-NaMnO2}$ pronounced? [closed]

I am a theoretical physicist, so I am not very familiar with chemical names. The material I am interested in is $\ce{\alpha-NaMnO2}$. Would that be pronounced alpha sodium manganese dioxide? Is it ...
10
votes
3answers
280 views

Is there any definitive evidence that implicit solvation methods are more accurate than explicit solvation methods for free energy calculations?

I am looking for real data that concludes that implicit solvent models are definitively better than explicit solvent models for solvation free energy calculations. The motivation is a lovely ...
11
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0answers
46 views

Discrepancy between numerical and transformed derivatives

This is related to a prior question of mine Derivatives with respect to user defined vibrational modes. While that one focuses on potential software to use for derivatives with respect to normal modes,...
15
votes
2answers
100 views

State of the art in computational materials design

With the advent of more computational power than ever in the recent years, interest in in silico design of interesting compounds has grown as well. I am wondering about the state of the art for the ...
13
votes
2answers
368 views

How to export a calculated Raman spectrum in Q-Chem, as a Gaussian profile?

Does anyone know how to export a calculated Raman spectrum (my calculation was performed in Q-Chem) as a data-file, which can be used to plot the profile of a Gaussian-shape spectrum (in origin, excel,...
8
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0answers
36 views

What is band inversion and how to recognize it in band structure?

Band inversion is a key ingredient of a topologically nontrivial material$^1$. What is band inversion? How to recognize it in a band structure? What conclusions can I infer if I observe band inversion ...
9
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0answers
17 views

Tools for Valleytronic Research

Similar to spintronics, which attempts to use electron spin polarization as the bits (or possibly qubits) in a logic device, valleytronics attempts to use a combination of the spin and "valleys" in ...
12
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0answers
52 views

Semi-empirical software for bands calculations

In Semiconductor Physics, one of the main parameters of interest is the band gap. It is known that, in DFT, there are functionals that underestimate it. I came across the MOPAC program, a semi-...

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