For questions seeking answers deduced from or composed of theories regarding the chemical substances and about models and methods of theoretical chemistry.

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2
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1answer
75 views

Do cyclic oxygen molecules exist and their theoretical stability?

Do oxygen molecules ever become cyclic shapes like carbon and other elements? Why doesn't oxygen form cyclic compounds? How stable would they be if they do exist. Especially more than 3 oxygens. ...
1
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0answers
51 views

What are the unsolved problems in quantum chemistry? [closed]

The question is not necessarily limited in quantum, but also computational and theoretical chemistry. Wikipedia listed a few https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_chemistry ...
0
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0answers
26 views

Why do ionisations from non-bonding orbitals result in little/no vibrational structure in a photoelectron spectrum?

I understand that ionisations from bonding and antibonding orbitals create vibrational structure from the Franck-Condon principle, resulting in a greater overlap integral between different vibrational ...
14
votes
4answers
180 views

Is it true that all of the physical laws and mathematics needed to describe chemistry are known?

This question comes from a rather famous quote by Paul Dirac which goes like this, The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of ...
0
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0answers
25 views

Conical intersection using GAMESS

I would like to know how to locate conical intersection using a GAMESS calculation. I really appreciate an example alone with this since I am a novice I do not have a clear idea among bunch of ...
0
votes
1answer
38 views

Model of London forces and Hydrogen Bonding; the question is carried on forward, partially, as a personal question, from another question [closed]

Does Model of London forces and Hydrogen Bonding are themselves complicated and require multiple sub-models and assisted theories to explain its correctness. I asked this question in the form ...
1
vote
0answers
57 views

How can I get rid of 700 million tons of chlorine gas?

I am conducting a thought experiment in which 40 million tons of hydrogen are supplied through saltwater electrolysis each year, creating 700 million tons of chlorine gas (Cl2) and 800 million tons of ...
3
votes
0answers
18 views

Dexamethasone radius of gyration source

I am looking for a source for the radius of gyration of dexamethasone in aqueous solution. Does anyone know where I could get it from? Even better would be an estimation of the Stokes radius, but the ...
2
votes
1answer
65 views

Is a strontium-fluorine battery the highest voltage battery using pure elements?

Strontium has a very low standard electrode potential and fluorine has a very high one. $$ E_{\ce{F2 + 2e^- -> 2F^-}} = 2.87\mathrm{V} $$ $$ E_{\ce{Sr -> Sr^+ + e^-}} = -4.10\mathrm{V} $$ In ...
0
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0answers
84 views

What does Molecular Orbital Theory get wrong?

I am learning about MO theory in my advanced inorganic chemistry course and am starting to realize that it is truly the most accurate representation of how molecular orbitals look like, where they are ...
1
vote
0answers
67 views

Warning during geometry optimization via Gaussian

I have some recurrent problem with my DFT calculations [functional: hseh1pbe; basis:6-31+g(d,p), object: porphyrin derivative]. During the MO setting I get: **** Warning!!: The largest alpha MO ...
7
votes
1answer
93 views

Ballistic behavior of molecules on potential energy surfaces

I came across the following sentence in a publication$^1$: "At this point we have to remember that the computed MEP path [sic] represents the reaction in the absence of any kinetic energy, while in ...
1
vote
0answers
41 views

Are empty orbitals degenerate?

This is apparently a true statement: "In a hydrogen atom, the 2s and 2p subshells have the same energy." Why is this the case? Why would they be of the same energy? Wouldn't the 2p be slightly ...
1
vote
0answers
41 views

Will there ever be a “last element”? [duplicate]

Recently the IUPAC added four new elements to the periodic table and it seems the race for discovering new elements is just getting faster. I was wondering if a "last element" exists; an element with ...
9
votes
1answer
119 views

Why does bond length decrease with increased basis set quality for SCF methods?

From Reviews in Computational Chemistry Vol. 5, for $\ce{H2O}$ using HF, MP2, CCSD, and CCSD(T), all lengths in angstroms: $$ \small \begin{array}{rcccc} \text{Basis} & \text{HF} & ...
0
votes
2answers
49 views

hydroxide ion in water — How does the dynamic change?

It's well known that $\ce{H+}$ ions in water always form $\ce{H3O+}$ ions. Likewise, $\ce{OH-}$ should exist always as $\ce{H3O2-}$ ion. If I am correct at this point, how would the dynamics be ...
1
vote
1answer
78 views

Nuclear zero-point energy and quantum delocalization effects of water molecules

What do we mean by "Nuclear zero-point energy" and "quantum delocalization effects" of water molecules ? It's said that without these effects "water" becomes somewhat unbounded, which is not very well ...
4
votes
1answer
81 views

pka from molecular dynamics

How can one calculate pKa values from first principle calculations, static or dynamics? I have encountered some works using CPMD where people try to find pKa values from -(i) constrained Molecular ...
1
vote
1answer
85 views

Confusion about atomic/molecular orbital terminology

I have come across several different orbital terms: atomic orbitals, natural orbitals, split-localized orbitals, molecule-intrinsic orbitals, quasi-atomic orbitals. I don't know what the difference ...
2
votes
1answer
131 views

What is the Franck-Condon region

What precisely is the Franck-Condon region? My understanding is that the FC region is the "bonding" or "equilibrium" region in a potential energy surface, i.e. near the minimum. But when a transition ...
3
votes
1answer
74 views

Calculating Raman Intensities from Static Raman Activities

Whenever I want to calculate a Raman spectrum, my quantum chemical programs give me Raman scattering activities. As the common Raman spectrum is dependent on the incident wavelength of the used laser ...
6
votes
4answers
3k views

How to calculate the concentration H3O+ in a solution with pH=6.99?

What is the correct way to calculate the concentration $\ce{H3O+}$ in a solution with $\ce{pH}=6.99$? Attempt 1. pH<7, therefore there are only $\ce{H3O+}$ particles in the solution. ...
2
votes
0answers
93 views

Why is conjugation not possible if there is not present alternate $\pi$ molecules according to MO theory?

I was reading this page at Chemwiki; there they were discussing conjugated-$\pi$ bond. In order to show that conjugation requires alternate double bonding, they cited the example of ...
4
votes
1answer
61 views

Is it possible to have accumulation of electron density in the inter-nuclear region even if the overlap integral is zero?

Recap: Lately, I've been studying Hückel theory where I learned about the approximation of neglecting all overlaps and making overlap matrix an identity matrix that is $S_{AB}= 0\;_; \;S_{AA}= 1$ or ...
8
votes
2answers
188 views

How can off-diagonal Hamiltonian matrix elements be nonzero when the overlap matrix is diagonal?

While studying about Hückel theory, I got accustomed to the approximation of making the overlap matrix an identity matrix; that is making the off-diagonal elements zero as $S_{AB}= S_{BA}= 0\;;$ this ...
2
votes
1answer
85 views

What is the reason behind neglecting & putting the overlap integrals $0$ in Simple Hückel Theory?

This is an excerpt about Simple Hückel Theory from Elements of Physical Chemistry by Peter Atkins: The first step that Hückel took was to ignore the $\sigma$-bonding framework and focus solely on ...
2
votes
1answer
52 views

What is the significance of Law of Multiple Proportions?

I cannot understand how the Law of Multiple Proportions is significant, or how does it further improve over Law of Conservation of Mass or Law of Definite Proportions. From Wikipedia: If two ...
3
votes
0answers
47 views

Coordinates for molecules except cartesian and zmatrix

Every program in theoretical chemistry that I know uses different ways of writing their input. The same holds true for writing the geometry of the molecules of interest. But they can all be reduced to ...
5
votes
1answer
79 views

Should I include solvation in quantum chemical calculations of a simplified protein-ligand interactions?

I am running a B3LYP-D3/6-31+G geometry optimization of a protein-ligand interaction. Well, not quite, I have simplified the protein to four amino acids surrounding the active site, but I keep the ...
4
votes
2answers
77 views

Do orbital models derive from the solution of the stationary Schrödinger equation?

I know that hydrogen-like atomic orbitals can be seen as a solution of the stationary Schrödinger equation - but what about atoms with more electrons? As I am a pupil and quite uneducated about this ...
3
votes
1answer
123 views

Suggestions for simulating transport through membranes with Molecular Dynamics (MD) and Monte Carlo (MC)?

I'm intending to perform a simulation of the transport of simple ions or water through perm-selective membranes, using Molecular Dynamics (MD) and/or Monte Carlo (MC). I've read around that, in ...
11
votes
1answer
150 views

How important is it that geometry be optimized at a high level of theory?

I've been doing research with a computational chemist for a little while now and in one of our projects we are dealing with a rather large system and because I go to a relatively small university, our ...
5
votes
3answers
71 views

Is there a universal minimum energy state?

I'm imagining this: if everything was separated (even on the nuclear level) and then the parts were recombined so that they were in the lowest possible energy state, do we have any way of knowing what ...
0
votes
1answer
58 views

Double bond equivalent [duplicate]

The formula for degrees of unsaturation is: $$1+ \frac{1}{2} \sum ( n_i (v_i-2))$$ $v_i$ = valency of atom $n_i$ = number of atoms with that valency Could someone explain how the formula works, ...
12
votes
2answers
890 views

Protons and the Heisenberg principle

The Heisenberg uncertainty principle implies that it is not possible to calculate the position and velocity of a body at the same time accurately. Electrons follow this principle since their orbitals ...
1
vote
1answer
108 views

Why do noble gases like Xe and Kr form compounds, despite offending the octet rule?

According to the octet rule noble gases should not form compounds but xenon and krypton form compounds like $\ce{XeF2}$, $\ce{XeF4}$, $\ce{XeOF2}$ and $\ce{KrF2}$ respectively. Why?
10
votes
1answer
185 views

Is it possible that atoms with 120 protons are possible, but that atoms with 119 protons aren't possible?

We currently know that there are atoms with atomic number up to 118 are possible. Is it possible that atoms with 120 protons are possible, but that atoms with 119 protons aren't possible? Or are ...
5
votes
1answer
94 views

Non-bonded orbitals in water

General Chemistry perspective: Looking at the molecular orbitals of water, we can see that the oxygen is $sp^3$ hybridized. Oxygen forms two sigma bonds with hydrogens, and there are two lone pair ...
4
votes
1answer
880 views

Definition of Electronic energy

Using Born-Oppenheimer approximation, we separate the nuclear and electronic parts of the wavefunction, and treat them separately. We include the terms that have direct dependence on the electronic ...
1
vote
1answer
69 views

Is anything ever proven in science? [closed]

People often say that nothing is proven in science. This is even true of well-supported theories and laws, which can supposedly be proved wrong with future advances in science and technology. ...
1
vote
0answers
112 views

Predict flame test color?

If you know the composition of any sample of compound, is it possible to predict it's flame test color? For eg, if you can given Sodium Chloride, then without actually doing the flame test, can you ...
0
votes
1answer
96 views

Why do we excite electrons before hybridisation?

In case of hybridisation like $\mathrm{sp^3}$ hybridisation of carbon or nitrogen why do we excite electrons before hybridisation? Why couldn't we just mix orbitals without exciting electrons?
1
vote
0answers
42 views

What is the justification for Ligand Close Packing Model?

The LCP model predicts that nonbonded atom to atom distances remain approximately the same when the central atoms are changed. What is the theoretical justification for this? thanks
6
votes
2answers
155 views

Freezing all the water on earth with a seed crystal

I was recently reading the satirical, fictional book Cat's Cradle by Kurt Vonnegut. In this book, one of the major subplots is the invention of a mythical polymorph of ice called ice-9 in the book. In ...
10
votes
2answers
261 views

Better functionals to work with transition metals

My Masters in inorganic chemistry is focused in magnetic properties of transition metals; great part of the work is done with DFT methods using softwares like ORCA and NWChem, but since my University ...
2
votes
0answers
41 views

What closure relations can we use in molecular modelling?

Following my question here about the BBGKY hierarchy I was wondering does anyone have any experience in using the method outlined. In particular how would I take an equation off the page and for some ...
7
votes
2answers
3k views

Why is CO practically nonpolar?

This question was in my book. According to me CO should be polar as it should have a dipole moment. But I found that the $\sigma$-electron drift from C to O is almost nullified by the $\pi$-electron ...
13
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2answers
1k views

Is Hydrogen Bonding a Type of Dipole Dipole Interaction?

I understand that dipole dipole forces is due to the attraction of the different partials charges of atoms in different molecules due to their different electro-negativities. For hydrogen bonding, ...
4
votes
1answer
46 views

Plasma creation and condensation

Every chemical has a decomposition temperature. My understanding is that above that temperature molecular bonds are broken. And if we raise the heat high enough then all molecular bonds will break ...
2
votes
0answers
140 views

kinetic reaction rate greater than extent of reaction for equilibrium

I'm comparing a model with chemistry at equilibrium versus a kinetic one. I take a network of two reactions: methane steam reforming (MSR) and water gas shift (WGS) at 700°C. I calculated extent of ...