Questions tagged [basis-sets]

For questions about the usage and construction of electronic structure basis sets.

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What would be the criteria for comparing basis set?

I have found that 6-31G* is similar to def2-SVP e.g.. What would be the criteria for comparing similar basis set?
Another.Chemist's user avatar
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SIESTA basis set optimization (Enthalpy vs total energy)

Using SIESTA for bulk Si (not optimized, downloaded from materialsproject.org), I am trying to optimize the DZP basis set using the PAO.EnergyShift parameter. ...
Mohamed Saleh's user avatar
4 votes
1 answer
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Computing energy and forces directly from machine learned wavefuntion/density

I have been reading up on methods where electron density was estimated directly from some machine learning method, followed by evaluation of energy and forces[1,2]. My understanding is that this is ...
ipcamit's user avatar
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Numerical atomic orbitals vs Gaussian-type orbitals for molecular calculations

Gaussian-type-orbitals (GTOs) are the work horse of modern molecular quantum chemistry calculations. They are computationally efficient and allow for analytic evaluation of integrals. However, there's ...
Fracton's user avatar
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Quantifying relativistic effects in DFT calculations

I am wondering what is the best approach to quantify the contribution of relativistic corrections to a result of an electronic structure calculation. As far as I understand, from a user perspective ...
Szgoger'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
4 votes
1 answer
415 views

Kill or let be: Is this calculation stuck or just very slow?

My question is regarding a medium-to-large DLPNO-UCCSD(T)-F12 calculation. I have a ~250 electron system, an open-shell molecule inside a water droplet, and I'm trying to get the total energy, first ...
epalos's user avatar
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Explicit form of Hartree Fock analytic gradient with contracted GTOs? With or without density fitting

Does anyone know of a paper, textbook, or other resource which outlines the expression for the analytic gradient of the HF energy (restricted or otherwise) in terms of Dunning's contracted Gaussian-...
Rob L's user avatar
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How to choose the orientation of basis functions in a Gaussian calculation?

I am trying to run a g09 calculation for a D5h symmetric molecule using the HF/LANL2DZ level of theory. The molecule is pentagonal planar in geometry, and I would like to visualize the canonical ...
Kevin Freddo's user avatar
3 votes
1 answer
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How to exploit STO-nG coefficients from basissetexchange (BSE)?

I am trying to understand how to use the data of STO-6G basis from BSE in order to code my own DFT package. I started with a simple DFT code for H2. So the primitive gaussians are of the from : $$\...
mle's user avatar
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How to remove f functions from a cc-pVQZ basis set in CFOUR format?

I need to perform a calculation on a BN system with using cc-pVQZ stripped of the f functions. However, I don't really know how to do this and I have not been able to find a revised one already. I ...
farmaceut's user avatar
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Help with Mathematica for optimizing a Gaussian basis set for a hydrogen atom in a magnetic field

This is a follow-up to my previous question: Optimal Gaussian basis set for hydrogen atom in magnetic field Brief description of the problem I would like to find the ground and excited states of the ...
Mam Mam's user avatar
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DFT calculation for conjugated polymers

I am new to DFT calculation. I want to know the structure of conjugated polymers (plane angle, etc.) and their electronic and optical properties (such as HOMO-LUMO, IR, etc.). I am using 6-311+G(d) ...
Duy-Minh Hoang's user avatar
7 votes
1 answer
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Optimal Gaussian basis set for hydrogen atom in magnetic field

Copy from here https://mathematica.stackexchange.com/questions/285044/optimal-basis-set-of-gaussian-functions-for-describing-a-quantum-system This question arose during the discussion of the previous ...
Mam Mam's user avatar
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What is the X in Almlöf and Taylor's "Unified treatment of energy derivatives?"

I have been studying the possible methods for basis set optimizations. One notable paper is "Energy-optimized GTO basis sets for LCAO Calculations. A Gradient Approach" by Knut Faegri Jr. ...
John's user avatar
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1 answer
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Choosing the right basis set for describing vdW-interactions with DFT-D3

I want to do some DFT calculations for structures of protonated alkaloid dimers. I know that a method of choice when vdW interactions are involved is the use of dispersion corrections. But now I am ...
C_Swann22's user avatar
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1 answer
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Inputting custom STO-3G basis into PySCF

A simple question about PySCF, but nonetheless I could not find out how to do it: I have a system of atoms for which I already calculated a STO-3G basis in the usual form of MOs: $$\chi = \sum_i c_i \...
greilchri's user avatar
2 votes
3 answers
132 views

Can I freeze f functions from a TZ basis set during MP2 (but not during H-F) to speed up calculations?

This is another question about my molecule; as I'm not doing this as an academical affiliate(I'm currently majoring in mathematics), I have only NWChem and my personal laptop on the mix, and thus need ...
Kanghun Kim's user avatar
7 votes
1 answer
187 views

Mixing pseudopotentials with gaussian and plane wave basis

I am somewhat of a novice in computational chemistry of materials, and have been tasked to replicate simulations from a relevant paper. The paper is a bit scant on details so I am trying to recreate ...
ipcamit's user avatar
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3 votes
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Does the accuracy of RI-MP2 follow the higher number of zetas of the main and fitting bases?

It has been answered to my previous question that RI-MP2/cc-pVTZ/cc-pVTZ gives results of the same quality as MP2/cc-pVTZ. I then started to think about RI-MP2/cc-pVTZ/cc-pVQZ. The term "basis ...
Kanghun Kim's user avatar
4 votes
3 answers
557 views

Does the RI method actually accelerate basis convergence of MP2, "by one more zeta"?

It is often said that the resolution of the identity (RI) method accelerates the basis set convergence rate of MP2 "by one more zeta", e.g. that RI-MP2/cc-pVTZ/cc-pVTZ results are close to ...
Kanghun Kim's user avatar
7 votes
2 answers
227 views

How does pyscf's internal basis format distinguish between 1s and 2s orbitals?

For example: gto.basis.load("6-31g", "Li") will show: ...
theQman's user avatar
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Do the cc/pc/def2 basis sets mathematically converge to the CBS limit, assuming exact CI/DFT?

The cc-, pc- and def2- basis sets are often described as "systematic", in the sense that the results of these basis sets at different cardinal numbers (i.e. the number of ζ's) can be ...
Kanghun Kim's user avatar
5 votes
1 answer
952 views

Choosing between 6-311++G(3df,3pd) and def2-TZVPPD for certain type of diffuse system

I need to use a diffuse basis set for my highly delocalised molecule, consisting of C, N, O, Cl, S, Mg, Al, B and Si only, since it has many non-covalent interactions inside it. After reading some ...
Kanghun Kim's user avatar
8 votes
2 answers
441 views

Basis Set to analyze a molecule that involves silver

I am a bit new to computational chemistry, but I've been looking into a reaction of a molecule that contains C, H, and F reacting with AgF in a polar solvent. I am looking into one pathway that ...
M.L's user avatar
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1 answer
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How to add different basis sets to different atoms in a calculation (Gaussian 16) when freezing certain atoms?

I am using Gaussian 16 to optimize a paraquat molecule on top of a bulk of gold atoms. Some of these gold atoms are frozen, so I use the option opt=modredundant. I ...
Anastasia Bitter's user avatar
5 votes
1 answer
183 views

What is the best algorithm for ERIs of contracted gaussian atomic orbitals

I am currently working on python script that does Hartree-Fock-Calculations. I try to avoid packages as good as possible. I've figured out how to calculate the one electron integrals when it comes to ...
lela2011's user avatar
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How exactly are valence orbitals combined in split valence basis sets such as 3-21G?

For hydrogen, the 3-21G basis set (in CFOUR format) is ...
theQman's user avatar
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9 votes
1 answer
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How to build cartesian representations of spherical Gaussian basis functions?

I'm trying to code an integral library for my own QC software from scratch. I need to use the spherical basis functions like in any other popular program. So, a D basis function is supposed to make ...
Dmitry Govorov's user avatar
5 votes
1 answer
157 views

How are the exponents in a STO-nG basis set obtained?

STO-3G has exponent parameters which can be found in a reference book. Can these parameters be calculated using, for instance, a Hartree–Fock equation for one atom? Or using another way?
SFriendly's user avatar
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1 answer
328 views

Basis sets optimized for CCSDT(Q) calculations

CCSDT(Q) and CCSDTQ calculations are extraordinarily expensive, both in terms of FLOP count and RAM capacity requirements, eg. CCSDTQ requires a computational effort that scales as ~$N^{10}$, where N ...
TiborGY's user avatar
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7 votes
1 answer
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Any molecular codes to calculate non-local susceptibility?

I am interested in calculating the non-interacting non-local susceptibility for simple molecules. In principle, if you have a single Slater determinant, then you should just take a sum over the ...
user avatar
5 votes
1 answer
93 views

About the order of indices in basis set expansion

In many books, e.g., Szabo and Ostlund, Helgaker Jorgensen and Olsen, etc etc, the expansion of Hartree-Fock orbital by basis set is written as a kind of $$ \phi_i = \sum_{\mu} C_{\mu i} \chi_{\mu} $$ ...
Lancashire3000's user avatar
9 votes
3 answers
402 views

The number of orbitals in Gaussian/GAMESS log file

After calculating the energy of a $\ce{CH4}$ molecule with a 6-31G(d,p) basis set, I obtained the Gaussian/GAMESS log file and describe a part of the log file as follows. ...
neco's user avatar
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5 votes
2 answers
633 views

The format and values provided by Basis Set Exchange

In this question and answers, I found that Basis Set Exchange provides information about the orbitals (e.g., the orbital exponents and contraction coefficients). For example, the following example is ...
neco's user avatar
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10 votes
4 answers
1k views

How can I find the parameters in a basis set?

I have a question about the basis functions of Gaussian. When the basis function is set (e.g., 6-31G), I would like to know the specific value of Gaussian's parameters for each atom. In particular, I ...
neco's user avatar
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11 votes
1 answer
601 views

What is the minimum basis set one should use?

If I'm interested in getting an answer that is minimally correct what is the minimum basis set level I should use? (i.e. anything less would be much less reliable) Obviously this depends on the ...
Cody Aldaz's user avatar
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How to get energy eigenstates using plane wave basis wavefunction .hdf5 output from Quantum ESPRESSO? [closed]

When compiled with the HDF5 flag on, Quantum ESPRESSO (QE) saves wavefunctions in the .save folder. At each k-point, we have an $m\times n$ matrix, where $m$ are the complex number entries of ...
TribalChief's user avatar
  • 2,351
8 votes
1 answer
266 views

Difference between original STO-3G and BSE STO-3G

I am trying to work with the STO-3G basis set, but I noticed that the STO-3G in Basis set exchange is different from the STO-3G originally published, and not only that, the BSE version seem to be ...
ipcamit's user avatar
  • 545
10 votes
1 answer
776 views

Molecular orbitals and active space

During the same minute as asking this question, I also asked this at Quantum Computing SE. In Qiskit, each qubit corresponds to one spin orbital. For example, the $\ce{N2}$ molecule would have 10 ...
ironmanaudi's user avatar
8 votes
2 answers
2k views

Is the number of basis functions same in the different atoms in the 6-31G basis set?

I'm now studying the quantum chemistry calculation and Gaussian basis set. For example, when using the 6-31G basis set, the C atom has 6 basis functions in 1s orbital: 3+1=4 in $2s$, 3+1=4 in $2p_x$, ...
neco's user avatar
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11 votes
2 answers
1k views

Critical difference and roles of Slater- and Gaussian-type orbitals

I was very interested in the following question and answer about the Slater- and Gaussian-type orbitals (STO and GTO) used in quantum chemistry and a practical calculation. Gaussian-type orbitals vs ...
neco's user avatar
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11 votes
0 answers
117 views

Should augmented basis be used for Hirshfeld charges? [closed]

I'm calculating condensed Fukui functions to explain the reactivity of my molecules. The manual for Multiwfn suggests using atomic dipole moment corrected Hirshfeld charges for it. However I get ...
Roman's user avatar
  • 2,373
7 votes
2 answers
178 views

What quantity to perform CBS extrapolation on for adsorption/binding energies?

When calculating complete basis set extrapolations for quantities, such as adsorption energies or binding energies, which depend on the difference between three quantities (i.e. $E_\textrm{prop} = E_\...
benshi97's user avatar
  • 408
10 votes
2 answers
140 views

How to create a differential spectrum from two simulated spectra, calculated by two different basis sets?

In my bachelor thesis, I compare simulated IR-spectra computed by different basis sets. The simulated spectra from sets like cc-pVTZ and cc-pVQZ are too similar to compare them by plotting them next ...
Till's user avatar
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8 votes
1 answer
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PES of Tetramethylthiuramdisulfid / Problem with Disulfidbridge

I like to perform a DFT Study on Tetramethylthiuramdisulfid. So I made a structure optimization for my start structur with PW6B95D3/aug-cc-pvtz to get a good structure to begin my dihedral scan to get ...
Andrea's user avatar
  • 856
17 votes
1 answer
3k views

Gaussian-type orbitals vs Slater-type orbitals in terms of computational efficiency

When creating molecular orbitals via the linear combination of atomic orbitals method I am told that Slater orbitals provide a more accurate representation whilst Gaussian orbitals are computationally ...
DJA's user avatar
  • 851
9 votes
1 answer
307 views

How are molecular orbitals constructed from the coefficients and basis set?

When an SCF calculation is done in a QM program, the MO coefficients of the solution are printed into the output. Now, graphical softwares can plot 3D molecular orbitals from these coefficients, ...
S R Maiti's user avatar
  • 6,841
14 votes
1 answer
145 views

What are the physical consequences of adding a constant to the diagonal of the effective Hamiltonian of monolayer materials?

Effective Hamiltonians modeling many-layered materials are often tuned using some sort of bias voltage. For instance, in a $4\times 4$ Hamiltonian matrix to describe biased bilayer graphene using some ...
TribalChief's user avatar
  • 2,351
17 votes
3 answers
881 views

How is "basis set projection" done?

I recently came across something called the basis set projection in Q-chem's manual. What it seems to do is to take the converged SCF in a smaller basis set, and then "projects" that onto a ...
S R Maiti's user avatar
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