Unanswered Questions
58 questions with no upvoted or accepted answers
22
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0
answers
248
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Is there a software that can do derivatives with respect to user defined vibrational modes?
I'm doing some property calculations that depend on a sum of derivatives of some quantity with respect to normal vibrational modes. I was hoping to find some physical intuition relating the type of ...
- 15.9k
9
votes
0
answers
184
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How to do parity analysis of band extrema?
To check whether electronic transitions are allowed between valence band maximum (VBM) and conduction band minimum (CBM) as per Laporte's rule, the parity of VBM/CBM is needed to be known. This paper ...
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7
votes
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answers
46
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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 ...
7
votes
0
answers
56
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Empirical approaches for predicting mass spectra
One way of predicting a mass spectrum of a new molecule is to run a semi-empirical BOMD computation where the molecule is ionized, gets a big energy and starts dissociating. However, I suppose that in ...
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7
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0
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179
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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 ...
6
votes
0
answers
71
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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 ...
- 6,804
6
votes
0
answers
105
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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 ...
- 20.1k
6
votes
0
answers
77
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Benchmarking DFT vs Experimental Gaps - Confusion over Fundamental and Optical Gaps
Recently, I've come across discussions about the differences between fundamental (or electronic) bandgaps and optical bandgaps, with the two quantities differing mainly by the electron-hole binding ...
- 1,366
5
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answers
57
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Do you have to rotate orbitals in a CASSCF calculation for each of the intermediates along a reaction?
I am trying out how to do CASSCF and I am computing the energies along a reaction.
I understand that CASSCF calculations may require orbital rotations, but how do I approach it if I am to do it across ...
- 141
5
votes
0
answers
50
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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, ...
5
votes
0
answers
124
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Geometry optimization with background charges in Gaussian with charge keyword
Gaussian requires the opt=z-matrix option when performing geometry optimization with the charge keyword. As can be seen in the following section from Gaussian's website:
To perform geometry ...
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5
votes
0
answers
129
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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 ...
- 129
5
votes
0
answers
77
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Can the electron charge density of two material systems be similar?
Broadly given two electron charge density (ECD) fields, is it possible to distinguish between the elements present in both the systems?
Since the ECD does not explicitly present any information on the ...
- 3,770
5
votes
0
answers
114
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How can one determine the time-step for imaginary time evolution?
The real-time evolution of a quantum system described by the state $\psi(t)$ is formally given by,
$$ \psi(t+\Delta t) = \exp^{- i \hat{H} \Delta t / \hbar} \psi(t)\tag{1}$$
For dynamical simulations ...
- 111
4
votes
0
answers
60
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How to plot orbitals for S1->T1 transition in Orca
I use TD-DFT and want to examine how molecular orbital changes upon ISC from S1 to Tx state and refer to confirm El Sayed rule. How to achieve it if NTO are not generated for S1->Tx transitions? If ...
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