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Questions tagged [quantum-chemistry]

For questions about quantum chemistry.

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Born oppenheimer approximation error

I got this exam question including BOA: 'rank the molecules according to increasing error value of the Born-Oppenheimer Approximation: H2, Cl2, F2, KCl, PtCl4, CH4'. my rank is: H2, CH4, F2, Cl2, KCl, ...
Jakub Spodenkiewicz's user avatar
2 votes
0 answers
39 views

Calculation of dipole moment from gaussian

I am trying to calculate the dipole moment of water molecule using Gaussian16. The problem I face is the use of Density=Current keyword in the route section. Here is the input file and output file ...
Pro's user avatar
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5 votes
0 answers
45 views

Geometry optimization with background charges in Gaussian with charge keyword

When I do geometry optimization with background charges in Gaussian, although the displacement values ​​converge, the maximum and rms force values ​​remain at a constant high value and the ...
padcrann's user avatar
3 votes
0 answers
17 views

DFT simulations of UV-VIS spectroscopy for Semiconducting Heterojunctions

I have a course project that involves DFT. Does anyone know of any tutorials or resources to simulate UV-Vis spectroscopy of semiconducting heterojunctions using ORCA, Quantum Espresso, or any other ...
user avatar
6 votes
1 answer
265 views

File extension difference of 'charge-density' file created by remote servers and personal computers

Recently, I ran an SCF calculation on a remote server, expecting to run an NSCF calculation afterward. So far, all the SCF calculations I have run on my personal computer have produced a 'charge-...
Thejan Hasaranga's user avatar
3 votes
1 answer
43 views

ERROR in NSCF calculation execution in QE

...
Thejan Hasaranga's user avatar
6 votes
1 answer
189 views

Using the same input (MINP) file, why does MRCC fail with a "normal" fort.55 file, but succeeds with a longer fort.55 file that has duplicate entries?

I have the following fort.55 file: ...
Jaafar Mehrez's user avatar
3 votes
1 answer
54 views

Why is the SCF calculation performed after VC-RELAX more energetically stable than the VC-RELAX calculation in QE

Recently, I performed a vc-relax calculation in QE. After vc-relax, I performed an scf calculation, including all the optimized parameters from the vc-relax output file (cell parameters, atomic ...
Thejan Hasaranga's user avatar
6 votes
0 answers
63 views

What matter modeling problems could be solved with 100 error-corrected qubits?

IBM, Infleqtion, QuEra, and other quantum hardware companies have announced roadmaps where they expect to have 100 or more error-corrected qubits by the end of the decade. It seems increasingly likely ...
taciteloquence's user avatar
1 vote
0 answers
36 views

Formation and Optimization of Dimers, Trimers, Tetramers, and Beyond

What is the procedure to follow in order to computationally create clusters such as dimers, trimers, or tetramers using Quantum ESPRESSO?
Thejan Hasaranga's user avatar
4 votes
0 answers
49 views

May I change the ICntrl variable in Gaussian 16?

Ive been trying to do energy calculations under the influence of a perturbative field with the BLYP and B3LYP functionals. Using the following input files: BLYP: ...
Atom's user avatar
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6 votes
1 answer
80 views

How to perform LC-BLYP calculation with GAMESS?

I am currently working on time-dependent density functional theory (TDDFT) calculations for both singlet and triplet states using the LC-BLYP functional in GAMESS. I believe I have correctly followed ...
Alireza Lashkaripour's user avatar
12 votes
4 answers
985 views

Are there non-antisymmetric solutions to the electronic Hamiltonian?

In electronic structure theory, one seeks solutions of the molecular electronic Hamiltonian $$ H_e(\vec{R}) = T_n(\vec{r}) + V_{ne}(\vec{r};\vec{R}) + V_{ee}(\vec{r}) + const, $$ where $\vec{r}$ are ...
Solarflare0's user avatar
8 votes
3 answers
217 views

Different results from MP2 calculations on same geometry in ORCA

I am trying to do a segmented potential energy scan around a dihedral for a molecule. I have optimized the geometry to a minima, and the scan runs from [-180, 180] in steps of two points at a time. ...
Hemanth Haridas's user avatar
4 votes
1 answer
54 views

Can we use formation/ cohesive energy to express the structural stability of a supercell?

I have created a graphene supercell using Quantum Espresso and performed a vc-relaxation on it. Now, I need to verify whether the created structure is stable and demonstrate its stability with ...
Thejan Hasaranga's user avatar
2 votes
0 answers
23 views

Why am I getting wrong information about basis functions on running gaussian calculation using the 6-31G basis set for the krypton atom?

This is the information about basis functions which I am getting on doing Gaussian calculation. But according to the best of my knowledge Kr has six primitive Gaussians for 1s, 2s,2p, 3s, and 3p ...
user avatar
3 votes
1 answer
74 views

Is there a minimum inter-defect distance when introducing point defects into a 2D structure, ensuring defects don't exhibit significant interactions?

I am currently conducting a DFT investigation into the magnetism of 2D materials by introducing defects into the structure. Is there a minimum distance I should maintain between two defects in ...
Thejan Hasaranga's user avatar
3 votes
1 answer
61 views

How is the form of the active space electronic Hamiltonian derived?

The electronic Hamiltonian in the canonical orbital basis has the following form: $$\tag{1} H_e = h_0 + \sum_{ij=1}^{N} h_{ij} \sum_{\sigma \in \{\uparrow,\downarrow\}} a_{i\sigma}^\dagger a_{j\sigma} ...
Solarflare0's user avatar
4 votes
0 answers
36 views

An excited state for a molecule, Molpro, casscf

I tried my best to bring an iodine molecule to an excited state to investigate orbital 4.3 but all my atteps were not successful. So, here is the file in molpro for the groundstate ...
Tkt's user avatar
  • 41
3 votes
1 answer
98 views

Orthonormality of AOs and MOs in PySCF

I have a basic question about how to calculate molecular-orbitals from atomic-orbitals in PySCF using the self-consistent field approach. My understanding mathematically is as follows: we start with a ...
Solarflare0's user avatar
5 votes
1 answer
188 views

Calculation of S1 energy in Gaussian

I am trying to calculate the energy of the S1 state with UDFT in Gaussian software. I understand that, generally, one should manipulate the charge and spin multiplicity to manually change the ...
Laura's user avatar
  • 1,267
2 votes
1 answer
332 views

'The combination of multiplicity electrons is impossible' in Gaussian

I am trying to calculate the energies of the S1 and T1 states of a molecule with UDFT using Gaussian. For the T1 state, I can successfully use the following input file: ...
Laura's user avatar
  • 1,267
5 votes
1 answer
40 views

How to Model Cations or Anions for Activation Energy Barrier Calculation in VASP for Electron Exchange Reactions?

I am interested in performing activation energy barrier calculations using VASP (Vienna Ab initio Simulation Package) specifically for reactions involving electron exchange. However, I am uncertain ...
Nidhi Tiwari's user avatar
7 votes
1 answer
355 views

Have quantum computers been proven to speed up any matter modeling algorithm?

Personally, I think quantum chemistry is one of the most promising applications for quantum computers because the problem itself is fundamentally quantum, so there is an obvious argument why we should ...
taciteloquence's user avatar
5 votes
0 answers
126 views

What are the most promising areas where quantum computers could advance quantum chemistry in the next 3-5 years?

A very similar question was asked about 4 years ago, but this is a fast moving field, so I think it warrants reexamining. What are the most promising areas where quantum computers could advance ...
taciteloquence's user avatar
1 vote
1 answer
91 views

How to use the CI method to compute the order of the molecular orbitals of the nitrogen molecule

It is well known that the Hartree–Fock (HF) approximation predicts a wrong order for the last two molecular orbitals of N$_{2}$. The calculations indicate that the 1$\pi_{u}$ orbital has higher energy ...
AlfredV's user avatar
  • 183
2 votes
1 answer
21 views

Geometry of H2O in the v=1 vibrational state for AIMD simulation

This is a follow-up to my recent question: Algorithm for finding the v=1 state of an H2O molecule I want the geometry (atomic positions) of the H2O molecule in the v=1 state. How are initial ...
Nidhi Tiwari's user avatar
1 vote
1 answer
28 views

Algorithm for finding the v=1 state of an H2O molecule

In the context of simulating the dissociation dynamics of an H₂O molecule on a metal surface, what algorithm is employed for generating the initial state of a tri-atomic non-linear molecule, such as H₂...
Nidhi Tiwari's user avatar
4 votes
1 answer
114 views

How to orthonormalize a set of Molecular orbitals?

I am using PySCF, and checked that the molecular orbitals(MO) from the HF calculation are orthonormal. If S is the Overlap matrix, and V is the matrix of the MO coefficients, It can be seen from the ...
Pro's user avatar
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7 votes
2 answers
171 views

Why is electron correlation called the "chemical glue"?

A significant part of quantum chemistry involves developing methods that go beyond the Hartree-Fock theory which treats electron-electron interactions through a mean-field approach. From what I ...
Fracton's user avatar
  • 271
2 votes
1 answer
138 views

How do I determine the charge and spin multiplicity of a system?

I have a compound (5c from here) as below which I wish to optimize in ORCA. However, I am not sure what is its charge and multiplicity. This is an Ir(III) complex. Iridium has a valence configuration ...
farmaceut's user avatar
3 votes
0 answers
45 views

Reproduce Dissociation Energy of BH molecule with PySCF

I want to reproduce the bond dissociation energy of the BH molecule as stated in the book 'Molecular Electronic Structure Theory' by Helgaker et al, (chapter 8.3.1), using FCI with 1 frozen core ...
jakg's user avatar
  • 31
7 votes
1 answer
78 views

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
  • 271
2 votes
1 answer
57 views

How can I calculate ionization energies and electron affinities with MOPAC?

can I simply calculate the ionization energy (IE) as the difference between the neutral and the charged system Heat of formation (Hf) with MOPAC ? The same question is with the electron affinity (EA). ...
Miro Iliaš's user avatar
3 votes
1 answer
104 views

How may I verify that my A matrix for TDA (Tamm-Dancoff Approximation of TD-DFT) from PySCF is correct?

This is a follow-up to a series of questions that I have asked here: Is a D-Wave quantum computer able to do TD-DFT calculations? (answer was "yes, but it might not be efficient") Inquiry ...
Hadeel Moustafa's user avatar
2 votes
0 answers
17 views

Can I define molecular units on NBO3.1 or NBO6.0?

I'm studying donor-acceptor charge transfer (CT) process between tetrakis(m2-acetato)-di-Wolframium (acceptor) with an acetonitrile (donor) at the B3LYP-D3BJ/def2-TZVPD level of theory. The W···N ...
Juandiego Velasquez Benites's user avatar
2 votes
0 answers
42 views

How to set up a calculation including dummy atoms in Dalton Quantum Chemistry Package?

I want to plot a magnetic shielding isosurface around benzene molecule, for that, I prepared a 100 atom grid keeping benzene at the center. At each grid point there is a dummy atom (X with charge=0.0)....
MeliodusSama's user avatar
6 votes
1 answer
94 views

Is it essential to include solvent cage effect in radical reactions?

My question is straightforward and is outlined in the post title: Is it essential to include the solvent cage effect in radical reactions during the computational estimation of Gibbs free energies and ...
farmaceut's user avatar
4 votes
0 answers
23 views

How to evaluate excited state MO coefficients using Dalton Pacakge?

I need the excited state (T1) wavefunction associated with my benzene molecule, but even after trying multiple times using multiple input formats, I am not able to find the correct input to evaluate ...
compcal's user avatar
  • 93
5 votes
1 answer
58 views

A matrix form used in the Quantum Annealer Eigensolver (QAE)

In the paper "Computing molecular excited states on a D‑Wave quantum annealer", PySCF is employed to compute the TDA matrix. Then a few of the lowest eigenvalues and eigenvectors of a TDA ...
Hadeel Moustafa's user avatar
4 votes
1 answer
115 views

Inquiry about A Matrix Output in 21-matrix_A_B.py

I'm trying to use the pyscf library for some calculations, specifically the 21-matrix_A_B.py example script for obtaining the A matrix. https://github.com/tepl/pyscf/blob/master/examples/tddft/21-...
Hadeel Moustafa's user avatar
4 votes
2 answers
206 views

Total energy calculation for an isolated atom

I tried calculating total energy using SCF calculations after optimization with quantum espresso. Still, I don't know how to optimize total energy in the standard state instead of isolated atoms. If ...
MALAK's user avatar
  • 43
4 votes
2 answers
160 views

Post-hartree fock calculation with localized Molecular orbitals in PySCF

I have localized the canonical Hartree-Fock orbitals for a molecule in PySCF. Now I want to perform ccsd calculations with these localized orbitals. Is it possible with pyscf? Example with CCSD with ...
Pro's user avatar
  • 1,024
3 votes
1 answer
182 views

Is a D-Wave quantum computer able to do TD-DFT calculations?

I was reading this paper (Computing molecular excited states on a D‑Wave quantum annealer) and wondering if I can make a QUBO model for the equations used in the TD-DFT energy calculation for the ...
Hadeel Moustafa's user avatar
3 votes
1 answer
106 views

What are the observables when a quantum system is comprised of orthogonal spacetimes? [closed]

We are given a system of three quantum domains A, B, and C with the following properties: (1) domains A and B are independent Hilbert spaces, each with their own space and time dimensions. Both are ...
RalphW's user avatar
  • 39
4 votes
1 answer
141 views

Spin-orbit coupling and lattice constant

Cross-posted on Chem.SE. Is there any evidence that spin-orbit coupling (SOC) leads to a crystal lattice distortion? Using Quantum Espresso and DFT, I am getting different relaxed lattice constants ...
freude's user avatar
  • 392
5 votes
1 answer
64 views

Is it possible to predict reduction reaction products with a Gaussian program?

In a molecular geometry calculation using a Gaussian program, can I see changes in bond lengths or changes in structure when one electron enters the molecule through a reduction reaction? for example, ...
Jay Kim's user avatar
  • 51
7 votes
0 answers
166 views

How do you calculate a full quartic force field for anharmonic frequencies?

I am an experimental chemist interested in anharmonicity—I am particularly interested in how to calculate anharmonic frequencies. The method I have the most experience with is (generalised) second ...
isolated matrix's user avatar
2 votes
1 answer
132 views

ORCA Error: NCalcs not set

I've been getting the following error whenever I use CCSD(T) and the ORCA Forums don't have an answer to this one: ...
znc204's user avatar
  • 63
4 votes
1 answer
448 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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