Unanswered Questions
1,300 questions with no upvoted or accepted answers
27
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How to calculate transition dipole moment from two known wavefunctions
I'm interested in calculating the transition dipole moment (TDM) from the information from two wavefunctions of different states. This is somewhat similar to calculating the molecular dipole moment ...
- 6,801
24
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What is d-orbital collapse?
When I was perusing the works of Schwarz on atomic structure, I came across the unfamiliar term of d-orbital collapse.
He describes it as a variation in energetic sequence from group 1 to 3 elements ...
- 60k
15
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357
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Rotation around CC bond in 1,2-dioxetane: transition states and local minimum structures
TLDR:
What: Potential energy surface associated with rotation around CC bond in the ring-opened version of 1,2-dioxetane.
How: State average(4)-CASSCF(12,10)/VTZP constrained geometry optimizations ...
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14
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405
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What is the largest coupled cluster calculation that has ever been done (as of March 2019)?
I am doing some research and trying to make sure the numbers I am reporting are accurate.
I found that the paper by Sylvetsky et. al. says:[1]
We were, however, able to complete a ...
- 44.3k
12
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Calculating Triplet-Triplet Spin-Orbit Coupling
According to the Q-Chem manual [1], the singlet-triplet spin-orbit couplings between a singlet excited state $I$ and a triplet excited state state $J$ is:
$$\langle\Phi_\text{singlet}^I|\hat{\mathrm H}...
12
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309
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Accuracy of quantum chemistry calculations on iodine neglecting relativistic effects
Triiodothyronine is a molecule with three iodine atoms. If we attempted to calculate its properties with ab initio methods like Hartree-Fock or more complicated ab initio methods which included ...
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11
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Understanding two-electron integrals in Gaussian 09
I was comparing the two-electron integrals (electron repulsion integrals, ERI) printed by various well-established packages (Gaussian, GAMESS, Molpro etc.) and observed that Gaussian is the oddball in ...
- 9,881
10
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Doubt in Zeeman effect for sodium spectrum
I am reading an atomic molecular physics book (for Indian universities). You may not familiar with it. But you can download it from the link if you wish.
So in the book it is mentioned that for normal ...
- 209
10
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141
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Using symmetry and group theory arguments to explain iron(II) in a tetrahedral crystal field
I am trying to figure out how to explain $1s \rightarrow 3d$ spectroscopic transitions for $\ce{Fe^{2+}}$ in $T_\mathrm{d}$ symmetry. These transitions make up the pre-edge region in K edge X-ray ...
- 101
10
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Why is the bond angle of N-N-N in hydrogen azide not 180 degrees?
Chen and Wang (2009) have reported an $\ce {N-N-N}$ bond angle in the hydrazoic acid molecule of $171.5$ degrees using B3LYP/6-311G** model. The wikipedia page for the molecule also reports a similar ...
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10
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In a molecular dynamics context, is the methyl rotation in propene a symmetric or asymmetric internal rotor?
In a prior question, I asked about the (a)symmetry of the potential energy surface of the methyl rotation of propene. In that context, the kinetic energy of the nuclear motions is of course assumed ...
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9
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answers
196
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Is there a reliable chemical theory that predicts pKa based on structure?
Obviously, there are general stability arguments that can be made to estimate relative pKas, such as evaluating the stability of the conjugate base of an acid, or thinking about how polarized the bond ...
- 38.4k
9
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430
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Vanishing integral rule for two-electron integrals
I understand the vanishing integral rule for a one-electron integral to be:
$$\langle i | \hat{O} | j \rangle = 0 \hspace{1cm} \mathrm{if} \hspace{0.2cm} \Gamma_O \neq \Gamma_i \otimes \Gamma_j$$
...
- 11.8k
9
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Quenching rates in nucleation MD simulations
I am trying to perform nucleation simulations with molecular dynamics. To prepare the metastable fluid, I am equilibrating at temperatures about 30 K above the melting temperature, and then "quenching"...
- 71.6k
9
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514
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multielectron spin-orbit coupling and energy level
For multi-electron atoms for which the Hamiltonian (including the spin-orbit coupling) reads
$$H=\sum_i T_i-Z\sum_i V_i+\sum_i V_i^{\text{s.o.}}+\sum_{i>j}V_{ij}$$
The $T_i$ are the kinetic ...
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