Questions tagged [orbitals]
For questions about properties and types of orbitals
69
questions
1
vote
1
answer
30
views
The theoretical electron momentum profiles using Gaussian16
I am trying to calculate theoretical electron momentum profiles (TMP) of individual orbitals of a molecule using Gaussian16 for theoretical calculation of electron momentum spectroscopy. I there a ...
Arka
3
votes
1
answer
51
views
What is the real form of p-type gaussian basis functions?
I am attempting to write my own Hartree-Fock program, and I am currently working on implementing the STO-3G basis set for a few atoms. For C, it is of the form
...
- 333
7
votes
0
answers
40
views
How to determine if hybridization takes place between orbitals in an ab initio calculation using Quantum ESPRESSO?
I'm using Quantum ESPRESSO to determine the electronic properties of systems. Now I want to confirm if hybridization takes place between orbitals. I have generated density of states and projected ...
- 453
1
vote
1
answer
60
views
Most up to date explanation explaining the stability of high spin multiplicity (multiplicity=2S+1 ) states? [closed]
https://en.wikipedia.org/wiki/Hund%27s_rules:
"However, accurate quantum-mechanical calculations (starting in the 1970s)... singly occupied orbitals are less effectively screened or shielded ...
- 11
0
votes
1
answer
58
views
In which irreducible representations shall I put the electrons in an F atom in PySCF?
I’m looking to complete ROHF energy calculations in PySCF for the F atom.
I need to update the irrep_nelec dictionary for F.
I know that the one for the O atom is:
...
- 11
6
votes
1
answer
218
views
What is the correct way to set up occupation for single atom in CFOUR software?
I am doing some calculations on single oxygen atom (O) using CFOUR. According to a previous answer to this question and according to how CFOUR treats non-Abelian groups, I am considering the (O) atom ...
- 3,535
5
votes
1
answer
178
views
Is the electron-electron interaction to blame, for the added complexity of using "orbitals" for an N-electron system?
In a one-electron system such as the H atom, we are able to say that the orbitals are valid wavefunctions. But for complex systems with N-electrons, I have heard people say that they are just ...
- 3,535
4
votes
1
answer
122
views
When orbitals are labeled based on their irreps in D2h, how are the orbitals ordered for an N atom?
I am performing calculations on a Nitrogen atom using CFOUR. A nitrogen atom has a point group of Dinfh, but CFOUR uses a lower symmetry of D2h instead. So, looking at the available Irreducible ...
- 4,036
15
votes
2
answers
2k
views
Why is my hydrogen energy not equal to -0.5 hartrees?
I'm trying to calculate the HOMO of various molecules in water solution. I first tried to see how PySCF calculates the HOMO of hydrogen. I ran the following code:
...
- 153
3
votes
1
answer
129
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 ...
- 379
3
votes
1
answer
93
views
How to get the HOMO/LUMO from spin up/down eigenvalues?
I'm working with OpenMX and see that I have eigenvalues in the output in two columns: one for spin up and one for spin down. How would I know what the total eigenvalue is? Would I just add them ...
- 133
4
votes
1
answer
178
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 ...
- 1,056
2
votes
1
answer
268
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 ...
- 51
7
votes
1
answer
92
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 ...
- 271
4
votes
1
answer
367
views
Finding HOMO/LUMO from SCF calculation: VASP
I'm running some SCF calculations in VASP, and when looking at the OUTCAR, I see that for each KPOINT there is a slightly different value for the HOMO/LUMO (looking at Band No. and Occupation values, ...
- 133
4
votes
0
answers
30
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 ...
- 93
3
votes
1
answer
76
views
Is there a way to add 4f-oribital information in Pseudopotential?
Now, I'm calculating with a Quantum Espresso program
I want to need Eu pseudopotential file with 4f orbital information. But I couldn't find that file, no matter how much I search on the internet. ...
- 183
4
votes
1
answer
299
views
How may I calculate atomic orbital energies using VASP?
I am trying to calculate the d orbital energy of the Cu single atom, like in this page, I have tried to use the Eigenband energies minus the vacuum energy level(about 0.007eV).
...
- 2,087
3
votes
1
answer
142
views
Verifying periodicity of crystalline orbital modulus in PySCF
I'm trying to verify that the modulus of the crystalline atomic/molecular orbitals computed by PySCF satisfy the correct periodicity condition for the supercell. I'm considering a hydrogen chain ...
- 161
1
vote
0
answers
33
views
Change bonding thresholds in NBO Calculations? [closed]
I'm looking at a system with really long bond lengths, and I'm trying to determine if there's any interaction at all between orbitals on two particular atoms.
I'm using NBO7 with the GENNBO interface, ...
- 11
2
votes
1
answer
74
views
Does the relaxed density (and therefore the relaxed orbitals) depend on the final energy in OO-DHDF+D calculations?
During an OO-RI-ωB97X-2-D2 calculation on ORCA, the non-dispersion-corrected OO-DHDF part of the calculation is performed, the D2 dispersion correction energy added to the resulting OO-DHDF energy, ...
- 870
3
votes
1
answer
197
views
How is the LUMO lower energy than the HOMO for triplet state restricted-open shell DFT calculation?
I recently ran a calculation using the ROB3LYP/LANL2DZ level of theory for a triplet spin molecule. While analyzing the results, the HOMO is doubly degenerate and the LUMO is singly degenerate. I ...
- 367
2
votes
1
answer
75
views
Is it possible to plot the pDOS or visualize the molecular orbitals from GAMESS outputs?
I'm using the GAMESS software and want to try to plot the pDOS for my systems and visualize the molecular orbitals. I was thinking I could get the data from one of the ...
- 133
3
votes
1
answer
350
views
How to get the crystal/ligand field splitting of d orbital of Fe complex using Quantum Espresso
So I am working with Quantum Espresso (6.5) and we have built a few square planar Fe complexes (to be specific $\ce{Fe(NH_2)_2(OH)_2}$ cis and trans), and we ran scf (self consistent calculation) and ...
5
votes
1
answer
647
views
How to plot HOMO-LUMO diagram using python?
I'm trying to create a HOMO-LUMO diagram for a presentation, similar to the below figure from ResearchGate. I would like to learn how to do this with Python if possible, since I know this language (...
- 855
6
votes
2
answers
157
views
NBO analysis of potentially hypervalent compounds
I know that one can determine which type of bond is present between different atoms in a molecule by analyzing the output of an NBO analysis. Furthermore the second order perturbation theory analysis ...
- 543
7
votes
1
answer
244
views
Spin-Orbit coupling effects in topological insulator Bi2Se3
I'm currently trying to understand this paper explaining the origin of band inversion in the topological insulator Bi2Se3. In Fig. 2 (see below) they explain by means of 4 steps how certain atomic (...
- 141
7
votes
1
answer
461
views
How is the zero energy defined for molecular orbitals?
In DFT and Hartree-Fock bonding orbitals have negative energies while antibonding orbitals have positive energies. Why is this the case? It seems this is due to the zero-point energy being defined for ...
- 390
1
vote
0
answers
61
views
Question on possible cancellations in the computation of Dyson orbitals from FCC/FCI wavefunctions [closed]
Dyson orbitals are mathematically meaningful, in the sense that they, unlike the DFT orbitals for instance, are actual observables of the wavefunction, instead of being "the other way around"...
- 870
4
votes
1
answer
418
views
How many electrons and orbitals should I include in a CASSCF calculation?
I'm interested in running CASSCF calculations to get a dissociation curve for a number of systems of the form: atom-atom, atom-diatomic or diatomic-diatomic (e.g. Li+ ... O-, K+ ... O2, or N(3-) ... ...
- 1,250
6
votes
1
answer
154
views
Importance of orbitals other than HOMO and LUMO
I know that the HOMO, LUMO, and its gap are useful in understanding the physical properties and chemical reactions of molecules.
Here, are there any phenomena in physics or chemistry that other ...
- 1,789
6
votes
0
answers
116
views
Basic but fundamental question on the extended Koopman theorem using Dyson orbitals [closed]
Let there be some ground-state N-electron species named A. A Dyson orbital for Q is defined as the overlap between Q and (Q with one electron removed). The extended Koopmans theorem now states that ...
- 870
4
votes
0
answers
76
views
Do the orbital energies of ground-state Dyson orbitals exactly capture arbitrary excitation energies and/or ionisation potentials/electron affinities? [closed]
According to an answer to my question on whether the Kohn-Sham orbital energies theoretically exactly capture arbitrary ionisation potentials and/or excitation energies, the answer is no for both ...
- 870
6
votes
2
answers
216
views
Closed-form expression for excitation energies, given the exact XC functional
In an answer to my question regarding the theoretical rigour in computing excitation energies using only the Kohn-Sham orbital energies, the rigour turned out to be nonexistent.
After looking this ...
- 870
3
votes
1
answer
172
views
How to determine the concrete value for the wavenumber in tight-binding approximation
As a simple problem setting,
consider a one-dimensional linear crystal of NaCl with only 1s orbitals,
where the atomic distance between Na and Cl is also assumed to be 0.5 Å
for simplicity (Fig. 1).
...
- 1,789
4
votes
1
answer
782
views
Molecular orbital values on grid points in PySCF?
I am looking for a way to easily evaluate individual molecular orbitals on a grid(assuming a single determinant method for now) in PySCF.
I am aware on how to generate efficient grids for real-space ...
- 624
4
votes
1
answer
206
views
What is the difference between NBO program and NBO that we find in Gaussian?
I'm a little bit lost with NBO (natural bond orbital) analysis in Gaussian. I was told that pop=NBO in Gaussian gives me the charges of atoms, but that the NBO ...
- 855
5
votes
1
answer
367
views
How can I distinguish between n, pi, pi* orbitals when looking for excited states?
I recently asked about how to distinguish between transition types. I got an answer there about determining the character or type of the orbitals.
My problem now is that I'm not sure how to determine ...
- 855
9
votes
1
answer
2k
views
How to select the projections and inner/outer window for Wannier90 calculations?
I am new to Wannier90 calculations. I am trying to obtain the Wannier functions and Wannier interpolated band structure.
But I am having a problem in setting the parameters like ...
- 2,631
10
votes
1
answer
473
views
How to calculate molecular orbitals of octaoxygen under high pressure?
This question about octaoxygen:
Why is octaoxygen diamagnetic?,
was asked in chemistry, but I really don't have an answer in terms of molecular orbitals. I think it could be a mixing of the O$_2$'s $\...
- 603
9
votes
1
answer
107
views
Too large value of s-orbital in near nucleus
After my previous question (here), I'm now studying the orbitals actually used in Gaussian through calculating them myself using Basis Set Exchange data. However, I found that some orbital exponents ...
- 1,789
9
votes
3
answers
455
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.
...
- 1,789
18
votes
1
answer
1k
views
Do we know for sure that all atomic and molecular wavefunctions decay exponentially as r goes to infinity?
Slater type orbitals (STO) are considered to be more accurate than gaussian type orbitals (GTO) for atomic and molecular QM calculations because - among other reasons - they decay with $e^{-\alpha r}$ ...
- 603
10
votes
0
answers
1k
views
How to visualize natural atomic orbitals from PySCF [closed]
I'm trying to visualize the different methods of getting localized orbital (LO) given in the User Guide. I went through the example, saved the orbitals as cube files, then opened the files in ...
- 303
8
votes
1
answer
72
views
Does the INIWAV tag in VASP assume that the wavefunctions are plane waves?
I am trying to figure out how to set the initial wavefunction in VASP, on the VASP wiki page of INIWAV, it is said that VASP would fill wavefunction arrays with random numbers.
...
- 2,087
8
votes
0
answers
107
views
Is the formula of a Dyson orbital independent of whether there is degeneracy or not in the HOMO of the neutral?
A Dyson orbital is defined as:
$$
\textrm{Dy}(x) = \int dx_1 \ldots dx_{N-1} \, (\Psi^+(x_1,\ldots,x_{N-1}))^* \, \Psi^0(x_1,\ldots,x_{N-1}, x),\tag{1}
$$
where $\Psi^0$ and $\Psi^+$ are the total ...
- 605
5
votes
1
answer
988
views
Modify ORCA orbitals for CASSCF
I have run a HF calculation on naphthalene and I have checked the MOs that have been obtained. Now, I have to select my active and inactive orbitals for CASCF(10,10). As there are 34 occupied orbitals,...
- 987
6
votes
0
answers
89
views
Confused by NBO output, due to missing bonds [closed]
I'm about to do an NBO analysis to evaluate bond characteristics in a novel transition-metal complex.
As I have never done anything like that, I tried to understand the basic output for an octahedral ...
- 331
10
votes
1
answer
216
views
Orthonormality of Kohn-Sham orbitals
I was wondering if Kohn-Sham orbitals corresponding to a different Bloch wavevector should be orthogonal? I know that we should have $$\int d \boldsymbol{r}\phi_i(\boldsymbol{r}) \phi_j^*(\boldsymbol{...
- 123
6
votes
0
answers
65
views
Orbital space clustering [closed]
I am interested in how the orbital space of a system can be partitioned into clusters.
I read reading 'Cluster many-body expansion: A many-body expansion of the electron correlation energy about a ...
- 2,177