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Questions tagged [ab-initio-calculations]

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

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How to reproduce 2D small-angle X-ray scattering (SAXS) interferogram of water via ab-initio MD methods?

I am trying to reproduce the 2D SAXS interference pattern of bulk water via ab initio MD methods as shown in the figure below: The main aim is to recreate figure (a) via averaging MD configurations ...
mykd's user avatar
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6 votes
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What are the parameters in PySCF's Selected Configuration Interaction code

Dear StackExchange Members, I'm using the native PySCF implementation of selected configuration interaction (SCI). However, I can't seem to find any documentation detailing the algorithm or various ...
AWPrentice's user avatar
5 votes
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What do Negative Atomic Orbital Contributions in a Mulliken Population Analysis mean?

I am performing a Mulliken population analysis (MPA) for a molecular system of interest (calculated with B3LYP/Def2-TZVP). I am analyzing the LCAO-MO coefficients/contributions associated with each &...
Kevin Freddo's user avatar
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Actual calculation of Coulomb energy in DFT softwares

I have a question about the actual calculation of classical Coulomb interaction term in density functional theory (DFT) softwares. Of course I understand the form Coulomb energy as: $\int\int \frac{\...
neco's user avatar
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4 votes
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Query regarding individual polarization calculation using CP2K

I am seeking assistance in calculating the individual polarization matrix from CP2K. While utilizing the Polar input under FORCE_EVAL -> PROPERTIES -> LINRES -> POLAR, I observed that the ...
Simantini Paul's user avatar
4 votes
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CCSD calculation between two orbitals

I am trying to calculate the CCSD energies between two orbitals. Suppose I have a system, ...
Pro's user avatar
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4 votes
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Photorealistic Rendering: How To?

i have started computationally modelling materials from first principles recently, my code of choice being VASP [6.1.0]. Recently i have come across this paper in Nature: DOI:10.1038/s41567-023-01960-...
F.N.'s user avatar
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Carbon Capture Research - Force Constants & Basis Sets

Greetings Matter Modeling, I'm researching carbon capture dynamics in the context of sorbent regeneration. The UN IPCC Net-Zero goal requires 75 Mt-CO₂/year captured by 2030. According to the IEA, we ...
Phill McGee's user avatar
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What kinds of calculations have to execute for obtaining the velocity of the chemical precipitation of some salt on a thread from a water-salt mix?

Some salt ($\ce{NaCl}$ or another one) of $m$ grams is dissolved in some water of $V$ liters. After mixing up, the substance looks transparent or to put it more exact as a chemical solution. Then a ...
SFriendly's user avatar
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4 votes
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Setting a frozen core in Molpro

I am carrying out a project which involves obtaining the RHF result and the integrals for the chromium dimer (Cr2) under Ahlrichs' SV basis. In the literature against which we attempt to benchmark, ...
Izzy Vang's user avatar
3 votes
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Clarification Needed about Topological Invariants

I am seeking clarification on whether choosing the appropriate topological invariants has any relation to the dimensionality of the system. I understand that in three-dimensional (3D) materials, the ...
Jaafar Mehrez's user avatar
3 votes
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What is a relaxed reduced density matrix?

I am trying to understand how to calculate electronic properties using reduced density matrices from electronic structure calculation. So far, I understand (I think) that for the expectation value of ...
Szgoger's user avatar
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Why do constrained geometry scans behave differently based on the starting conformation?

In relation to my previous questions here and here, I figured that orca would be a better choice for my calculations. This was partly due to the inability of psi4 to converge to a minimum at many of ...
Hemanth Haridas's user avatar
2 votes
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Error in VASP calculation

I have been trying to do Piezoelectric and Elastic calculations for my system in VASP, and i ended up with this error. Spin polarized Harris functional is a good joke What am I doing wrong? Here is ...
Vivek karunakaran's user avatar
2 votes
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BURAI eliminates atoms when I try to modify the input file

I'd like to get the monolayer input file for MoS2 using BURAI 1.3. I downloaded the .cif file from Materials Project and with the Modeler function I created a Monolayer MoS2 but when I clicked "...
CoolerThanACooler's user avatar