Questions tagged [from-chem-se]

Questions that were first asked on Chemistry Stack Exchange.

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1 answer
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Exploiting 8-fold symmetry of ERI tensor for building Coulomb and Exchange matrices

I'm trying to write a restricted Hartree Fock code in Fortran that reads in a file of zeroth-iteration 1 and 2 electron integrals (FCIDUMP format) and uses them to do the SCF procedure from an initial ...
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7 votes
2 answers
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What is the real reason behind the minimization of the system at the beginning of a Car-Parrinello MD calculation?

I've been studying MD and more specifically about Car-Parrinello Molecular Dynamics and I'm not entirely sure if I understood the meaning behind the minimization. This is the way I understand it: The ...
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5 votes
0 answers
37 views

How do I model drug diffusion from polymeric matrix? [closed]

I have been redirected to this forum from Chemistry SE. My problem consists of a structure (say a cylinder) made from a homogenous distribution of a drug from a polymeric matrix. These compounds are ...
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12 votes
2 answers
251 views

What are the references in multi-reference methods?

After reading What exactly is meant by 'multi-configurational' and 'multireference'? I still don't understand what the multiple "references" are. I understand that you can for example use a ...
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5 votes
0 answers
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Predict the density of states (DOS) diagram for rhenium oxide (ReO3) from the molecular orbital diagram [closed]

Yesterday I made this query on Chemistry Stack Exchange, and a user has felt that perhaps here I will get a quicker answer. The structure of rhenium(VI) oxide, $\ce{ReO3}$, is similar to that of ...
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  • 451
7 votes
1 answer
209 views

How to generate Electron Density Fields using DFT?

How may I generate Electron Density Field information using Density Functional Theory calculations? What would my required inputs be like in VASP or Quantum ESPRESSO?
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9 votes
1 answer
184 views

How do I create geometry files for carbon nanoribbons and molecular junctions for DFTB+?

I am currently learning DFTB+ using the tutorials on the official website : Carbon Nanoribbons : https://dftbplus-recipes.readthedocs.io/en/latest/defect/carbon2d-elec.html#zigzag-nanoribbon ...
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9 votes
1 answer
204 views

Problem obtaining a Raman spectra of a graphene structure

I am trying to obtain the Raman spectra of a graphene structure using Gaussian. I used the input below, but when I did it, I got this error: ...
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  • 193
7 votes
1 answer
114 views

What does "Test job not archived" mean?

I am running frequency computation with geom=connectivity in Gaussian. It all converges now but at the very end of the last convergence it says: ...
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  • 135
6 votes
1 answer
190 views

Gaussian: Transition state convergence question

I am running a TS computation in Gaussian 16. It performs several steps. At the end of each there is a summary on whether Maximum Force, ...
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  • 135
13 votes
1 answer
266 views

How to determine which levels correspond to each other in LS coupling and jj-coupling?

In the LS coupling scheme, L, S and J are good quantum numbers; whereas in jj-coupling scheme, j1, j2 and J are good quantum numbers. I have learnt how to get the term symbols for LS coupling, and for ...
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20 votes
4 answers
3k views

Solving the Schrödinger equation as a service?

Does anyone know of a company with a cloud-based service which takes some representation of a molecule as an input, and then somehow solves the Schrödinger equation to some level of accuracy and ...
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  • 371
12 votes
1 answer
132 views

Metropolis algorithm reduces energy in molecular simulation, but does not decrease euclidean distance

I am using an open source python package openmmtools to run a simple molecular simulation problem using the metropolis algorithm. I first load a default system of particles (alanine-dipeptide in ...
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  • 123
10 votes
1 answer
149 views

Calculating/Visualizing electronic density from orbital information written in the Molden format

I'm trying to obtain an electron density from orbital information written in the Molden format by the formula, $$ \rho(\mathbf{r}) = \sum_{i}^{occ} |\phi_{i}(\mathbf{r})|^{2}. \tag{1} $$ Is there any ...
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  • 275
13 votes
2 answers
1k views

How many spin states do Cu+ and Cu2+ have and why?

I know an electron can have two spin states, "spin up" and "spin down", but recently I was asked how many spin states do $\ce{Cu^+}$ and $\ce{Cu^{2+}}$ have, and why? Does anyone ...
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  • 139
9 votes
2 answers
181 views

How to build a simulation model for a molecular dynamics simulation

I have got aggregate of 4 non-protein compounds I would submit for molecular dynamics simulation. The problem is I can't find software capable to do that. Amber, GROMACS, LAMMPS, all of them require ...
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10 votes
1 answer
370 views

Get fractional coordinates from special Wyckoff positions

I'm trying to get the fractional coordinates for $\ce{Mo}$ and $\ce{MoS_2-2H}$ in $\ce{MoS_2-2H}$, where 2H is the phase. $\ce{MoS_2-2H}$ is a bilayer, in which each layer is separated from each other ...
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14 votes
1 answer
250 views

Software to draw 3d micelle configuration

I am looking for a free software able to draw 3d micelle configuration like the figure attached. Any suggestion?
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11 votes
2 answers
315 views

One-center two-electron integrals between 1s STO

As per @user1271772 's suggestion I am asking this question here again. I am trying to understand SCF cycle by trying to code up solved example from Quantum Chemistry by Levine (page 443, 5th edition)...
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  • 295
18 votes
1 answer
669 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, ...
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  • 495
27 votes
3 answers
2k 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 ...
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  • 1,940
17 votes
1 answer
461 views

Alternatives to VEDA 4 vibrational energy distribution analysis software?

Said software is useful when you need to assign the peaks in vibrational spectra to different vibrational modes found in a hessian calculation for a given molecule, as described in Jamróz, Michał H. “...
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  • 3,696
28 votes
1 answer
954 views

Approximate equivalence table between Pople's basis sets and Jensen's DFT optimized polarization consistent basis sets (pcseg-n)

At first I posted this question in chemistry.stackexchange.com, before materials.stackexchange.com was launched in beta. As it went unaswered, I'm giving a try here. I have some calculations results ...
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  • 3,696
18 votes
1 answer
210 views

Exchange-Correlation Two-Electron Integrals

Do any freely available or proprietary electronic structure packages explicitly compute two-electron exchange correlation integrals? I have found a few derivations to calculate excited state ...
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19 votes
1 answer
124 views

Computational tool for identification of activity cliff

Activity cliffs are defined as pairs of similar compounds with substantial differences in activity (Molecular Diversity, 19, 1021–1035 (2015)). Are there computational tools for the identification of ...
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