All Questions
Tagged with quantum-chemistry molecular-structure
34
questions
1
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0
answers
58
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Reproducing Hydrogen Molecule Hamiltonian in OpenFermion
I am learning quantum chemistry at the moment and I'm trying to understand the Hamiltonian generated by the OpenFermion package. I'm now stuck at understanding how openfermion calculates the ...
- 11
4
votes
1
answer
265
views
Self Consistent Field method and LCAO
I am reading about the Self Consistent Field Method and Linear Combination of Atomic Orbitals.
Suppose we have one electron and one nucleus, then we can solve the Schrodinger equation explicitly.
If ...
- 43
-1
votes
1
answer
53
views
Analog of chemical accuracy in vibronic energy calculation [closed]
Is there any analog of chemical accuracy in vibronic energy calculation? I understand that the unit is /cm however, probably, I shouldn't expect a given number in that unit as the analog.
I am ...
- 245
2
votes
0
answers
36
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How do the spin-matrices change in systems without spherical symmetry?
The (non-relativistic) spin matrices of a free electron, with $z$ as the quantization axis, read:
$$
\boldsymbol{S}_{x}=\frac{\hbar}{2}\left[\begin{array}{ll}
0 & 1 \\
1 & 0
\end{array}\right],...
- 181
3
votes
1
answer
293
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In the LCAO method for $H_2^+$, why do we only add or subtract orbitals but never alter one of the phases of the orbitals?
TLDR:
Atkins' physical chemistry contains the quote "In general, from N atomic orbitals we can build N molecular orbitals". In the case of $H^+_2$, we use a combination of N=2 orbitals to ...
- 241
1
vote
1
answer
338
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Does anyone know what program was used to make this molecular structure picture? [closed]
I am a quantum chemistry beginer, and this picture color scheme is classic. I wonder how to make such pictures by myself.
3
votes
1
answer
483
views
Is it rigorous enough to change a DFT functional after geometry optimization to calculate excited state properties?
I have done the geometry optimization with the B3LYP functional, however, there is a need to calculate the excited state energy, so the CAM-B3LYP functional should be better suited for that. Do I need ...
- 77
1
vote
1
answer
1k
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Do changing opt=modredundant to opt in Gaussian makes geometry optimization not to take into account frozen angles?
I am a newbie to Gaussian and just generated an input for the geometry optimization for some molecules with multi ring system. However, in the article that was a reference for those calculations, some ...
- 77
3
votes
2
answers
427
views
Effective core potential and Gaussian basis set
Is using the effective core potential (ECP) and Gaussian basis set simultaneously in ab initio calculation a valid approach? For example, is it correct to use ECP for one of the atoms and, instead of ...
- 123
0
votes
0
answers
233
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Normal (Regular) or Inverted Terms?
I have a question on the order of the spin-orbit molecular states. I understand how to find the terms that split from a parent molecular state in a diatomic molecule. But my question is on how to find ...
- 167
1
vote
0
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151
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Cross-conjugation and aromaticity in pyrene
I have read about non-huckel double bonds and clar's rule, but what made me confuse is that huckel's perception gives me the feeling that central bonds in polycyclic aromatic hydrocarbons (ex: pyrene) ...
- 565
2
votes
1
answer
2k
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How to control the optimization step size in Gaussian?
I would like to perform a geometry optimization for a weakly bound methane dimer structure with Gaussian 16. During this process, the Newton-Raphson step should be controlled such that its length ...
- 243
0
votes
0
answers
416
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Probability density of a particle in a 2D box with given coordinates
Wavefunction of particle in a $2$D box with sides $L$ in the $x$ and $y$-axis:
$$φ = \sqrt{\frac {4}{L^2}} \sin\frac{n_1πx}{L}\sin\frac{n_2πy}{L}$$
For the different states ($n_1=1$, $n_2=2$), (...
- 1,095
0
votes
1
answer
160
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What's the definition for mole before Avogadro's constant?
I have been searching for about 3 days how Avogadro's constant is found, and as all of us know the value is determined by division of charge of one mole of electrons (Faraday's constant) by the charge ...
7
votes
1
answer
903
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Optimization completed on the basis of negligible forces
I am performing relaxed scan in Gaussian (B3LYP/6-31G(d,p)). There are two small organic molecules, one of which is a radical, the other has a benzene ring.
I'm trying to understand the optimization ...
- 229