Quantum chemistry is a subfield of quantum mechanics. Like the parent it focuses on physical phenomena that occur at an atomic scale, usually specifically aiming at chemical reactions.

learn more… | top users | synonyms (1)

2
votes
2answers
35 views

How are nuclei stable?

We all know that the density of the nucleus is very high. Nuclei are made up of protons and neutrons, and while protons have the same charge, they are closely packed in a nucleus. How does the ...
2
votes
0answers
16 views

Slater determinant as an unperturbed atomic wave function

I've deduced following postulates from studying my chem books. 1) Slater determinants are eigenfunctions of an unperturbed atomic Hamiltonian, which contains kinetic and central potential energy ...
0
votes
0answers
20 views

Behaviour of a “Black body ” [on hold]

Here is an another crazy doubt.... We all know that a black body can emit all the radiation which it absorbs.Sun is also a black body and it emits lot of radiation.. My question is "what is the source ...
3
votes
1answer
213 views

Totally confused about the location of “s,p,d,f” Orbitals inside the atom

Here is the other crazy question... I know that electrons revolve around nucleus in their orbits.But my question is "how the orbitals are located in the orbits? Do they really posses Spherical, dumb ...
1
vote
1answer
28 views

Is it possible to calculate atomic radius with electron configuration?

I need to know whether is it possible to calculate the atomic radius according to the number of electrons and electron configuration. Or is there any way to calculate the atomic radius using common ...
4
votes
1answer
117 views

why do 2 atomic orbitals form 2 molecular orbitals?

According to molecular orbital theory, two atomic orbitals form two molecular orbitals analogous to waves combining constructively or destructively but how can a wave combine destructively and ...
4
votes
1answer
59 views

What properties of an element determines the maximum number of bonds it can make?

From my conjecture, I think it's a mix between valence electron and the principal energy state, but I'm not sure. For example, C, N, O and F can only make a maximum of four bonds, as they can only ...
3
votes
0answers
52 views

Why do middle school and high school chemistry classes teach students that electrons are little balls? [closed]

When I was in high school, I took two chemistry courses. The first was very elementary and didn't attempt to move beyond the picture of electrons, protons, and neutrons as little balls essentially. ...
7
votes
2answers
89 views

Is it likely that increased understanding of quantum physics will change our understanding of chemistry?

Reading that the large hadron collider will be up and running with twice as much energy in March 2015, I was curious whether our understanding of subatomic particles has changed our understanding of ...
-1
votes
1answer
46 views

Why the second ionization energy of helium is greater than the first? [closed]

maybe because the first electron has a lower energy. Why does this happen?
3
votes
1answer
56 views

Unitary Transformation of the HF equations

I am working on a code to preform a HF procedure and I am a bit confused about the unitary transformation of the basis. My instructions are as follows. specify the basis and geometry (done) ...
1
vote
1answer
38 views

What are the molecular orbitals of the hypothetical linear H₃⁺ molecule?

What would be the wave function of the lowest energy molecular orbital of a hypothetical linear H3+ molecule? According to the LCAO method, I feel the lowest energy MO will be 1s(A) + 1s(B) + 1s(C). ...
1
vote
1answer
46 views

What effects do an electron in the nucleus have?

Under the understanding of quantum chemistry: There is a very miniscule chance that an electron could appear inside the nucleus of an atom. What could possibly happen if this "phenomenon" were ...
3
votes
2answers
72 views

What do short-range and long-range corrections mean in DFT methods?

Currently I am looking for the most accurate calculation method for a simple non-conjugate molecule consist of C, N, O and H. Normally I would try each method for a similar and known molecule then ...
2
votes
1answer
30 views

How is 2D spectroscopy able to show quantum coherent transport through networks?

For wave-like (quantum coherent) energy transfer in networks (eg. propagation of excitation in photosynthetic protein complexes of algae or FMO complex in plants) 2D electronic (photon echo?) ...
3
votes
2answers
131 views

How to simulate chemical reactions in GAMESS?

I am rather newbie in GAMESS field but finally could learn to make input files for most molecular simulations and even could use TD-DFT and excited states ( special thanks to Geoff Hutchison for his ...
3
votes
1answer
27 views

Non stationary effects of molecular orbitals

We have been learning a bit about molecular orbitals in class. However, we have always considered things under a quasistatic approximation. What are some effects that can only be explained by not ...
3
votes
1answer
53 views

Relativistic effects and lanthanide contraction

So I understand than the lanthanide contraction is due to poor shielding of the 4f electrons which decreases the radius. However, if Im not mistaken the relativistic effects lead to a contraction of ...
1
vote
1answer
35 views

What is the difference between Dielectric and Capacitive Polarizable Continuum Model?

I have good background knowledge on Quantum Chemistry calculations but my knowledge on Solvation Models is not that amazing ! Many times I read a paper that uses TD-DFT, they also assign some solvent ...
6
votes
1answer
112 views

Born-Oppenheimer Approximation reloaded

I'm an undergraduate Chemistry student and I'm currently writing my Final Dissertation. I've written a form of the Born-Oppenheimer approximation with the only initial assumption of parametric ...
3
votes
1answer
74 views

Why do principal energy levels in an atom get closer together as n increases?

The title says it all. Reasons that I can supply include: increased nuclear charge increasingly catches up in terms of influence to the increasing shielding and proof by contradiction in that if the ...
0
votes
1answer
42 views

Gaussian Calculations - What is the Basis?

What am I actually changing when I click 631G(d) or 631G(d,p), etc. when I choose a "basis" in restricted Hartree Fock calculations? What is the difference between using an alternative basis? Many ...
2
votes
1answer
171 views

The “rules” for LCAOs in Molecular Orbital Theory

In our course on physical chemistry, which involves MOT, we have been taught that in the LCAO approach, the wave function for a molecule... say hydrogen ion, can be approximated by a linear ...
1
vote
0answers
24 views

Dissociation of water into H+ and OH-: Does the law of mass action hold at nanoscale?

Suppose water under neutral conditions is confined in a virtual spherical nanocontainer with a radius of 25 nm. To calculate the number of hydronium ions, one uses water dissociation constant which is ...
1
vote
2answers
95 views

Is there any free GAMESS input file maker for Mac OS?

My main purpose is to simulate excited state calculations on a molecule with Time Dependent DFT. I am looking for free software that makes input files for GAMESS. I have tried Avogadro and it works ...
6
votes
1answer
138 views

Acidity of substituted phenols

Phenol has a $pK_{a}$ approximately equal to $9.9$. When one studies the acidity of chlorophenols, one notices the following: First of all, chlorophenols are more acidic than phenol, due the ...
6
votes
1answer
138 views

How does the radial distribution function of Vanadium differ from that of Calcium and how does this affect the ionic electron configurations?

When Vanadium is ionised it loses the 4s electron first, meaning that it's 3+ ion has a different electron configuration to Calcium despite it being isoelectronic. Can it be explained in terms of ...
0
votes
0answers
23 views

Using knowledge of radial distribution functions, how is it possible to explain the different electron configurations of V3+ and Calcium [duplicate]

I recognize that the 3d orbital decreases in energy to lower than the 4s once it becomes occupied (even if I don't completely understand why?!). However, how is the difference in electron ...
3
votes
1answer
86 views

Why are all the orbitals that have the same principal number in Hydrogen degenerate?

In hydrogen, all orbitals with the same principal quantum number 'n' (1,2,3...) are degenerate, regardless of the orbital angular momentum quantum number'l' (0,1...n-1 or s,p,d..). However, in atoms ...
5
votes
1answer
165 views

Interpretation of TD-DFT results

For the first time I'm doing TD-DFT calculations (wB97XD functional) in Gaussian 09 for an open-shell system and the results look like the hell of a mess for me. The molecule is rather big, so I ...
2
votes
1answer
51 views

Orbital angular momentum

For hydrogen atom, L^2 and Lz can be obtained as eigenvalues for a particular wave function. But that does not completely specify the angular momentum vector. How to get about this problem? Also, in ...
0
votes
0answers
26 views

Orbital representations [duplicate]

The usual 'orbitals' that we draw are drawn with the axes shown and everything. But orbitals are really only 1 electron wave functions of 3 dimensions... Therefore, they can't be plotted as such in ...
6
votes
2answers
2k views

Difference between shells, subshells and orbitals

What are the definitions of these three things and how are they related? I've tried looking online but there is no concrete answer online for this question.
5
votes
3answers
192 views

How is the bond length calculated from the total electronic energy?

In the quantum chemistry course that I currently attend, it was said several times that one of the key quantities derived from molecules by means of computation is the total electronic energy ...
0
votes
0answers
121 views

How to Locate the Excited State Dipole Moment in Turbomole Output (TD-DFT)

I want to calculate the dipole moment for the first excited state with a Q.C. program (TURBOMOLE: TD-DFT). The calculation lists the following output: ground state total dipole moment: ...
2
votes
0answers
34 views

Interpreting the MOs of a molecule

I've been looking at the MO:s of different molecules in Avogadro, fascinated by their magnificent geometries. But how is one supposed to interpret them, so as to understand their reactivity? What are ...
5
votes
1answer
171 views

Show the vibrational frequency of F2- is much lower than that of F2

Basically I need to draw the molecular orbital for $\ce{F2}$ and then answer a bunch of questions about it. I have drawn it correctly, as far as I know, but I don't know how to use it to show that the ...
9
votes
2answers
2k views

Why do atoms “want” to have a full outer shell?

Okay, so I know that this is about filling the orbitals of the atom, and I understand that. What I don't understand is why? For example, an Oxygen atom has 8 protons and 8 electrons spinning around ...
0
votes
0answers
37 views

Conical intersections - phase

Can anyone explain why at a conical intersection the wavefunction changes sign? My understanding is that it is a test to see if the crossing IS indeed a conical intersection or just a coincidence of ...
5
votes
2answers
196 views

Methods for Determining Partial Charges

I want to run classical molecular dynamics simulations of a periodically replicated surface (rutile $\ce{TiO2}$ with grooves). In order to do so, I first need to solve for the partial charges residing ...
6
votes
2answers
415 views

How does a Frost diagram reproduce the solutions to the wave equation?

I came across a Frost diagram for cyclic compounds in my book, and all my book had to offer was that it geometrically reproduces the solutions of the wave equation, and can therefore determine the ...
6
votes
4answers
526 views

Mathematics in inorganic and quantum chemistry

Is mathematics important to learn concepts in inorganic chemistry, such as point groups, point symmetry, because doing these topics requires one to determine the symmetry of the elements and to ...
16
votes
4answers
426 views

How Quantum Software Packages Work?

If one wants to calculate a moderate size Alkane ( with say 10-15 Carbons , assuming 100 electrons , with Restricted Hartree Fock based methods ) we can simply say that electron-electron part will be ...
1
vote
1answer
44 views

What is the wave function? [duplicate]

I understand that the square of the wave function is the probability density of finding an electron. However, what is the wave function itself? I am trying to understand molecular orbital theory but ...
2
votes
1answer
96 views

Differential Geometry in Chemistry?

I'm wondering is there any branches of Chemistry that make use of manifolds, Riemann geometry, tensors etc. So far I have not come across anything but hoped that the wider community would know of ...
1
vote
1answer
96 views

GAMESS crash course?

I'm still learning about MO theory – and I thought that I would do some calculations with GAMESS to become more familiar with the concept. Even though I look forward to delving into the realm of ...
-1
votes
1answer
64 views

If the electron of a hydrogen atom transitions from energy level n=5 to n=3, which level corresponds to n1 and which level corresponds to n2 [duplicate]

which level corresponds to n1 and which level corresponds to n2 in the Rydberg equation?
6
votes
2answers
1k views

How do we know that hydrogen gas consists of two hydrogen atoms?

Of course I know that both 1s orbitals will combine and that the electrons will occupy the bonding MO and that the two atoms will reach a lower energy state – but how do we really know that is the ...
4
votes
3answers
152 views

What actually is the Wavefunction?

I am aware that the square of the Wavefunction gives the probability density of finding an electron at a particular point in space. I have also heard that it's a complex number but since it's a ...
6
votes
2answers
1k views

Heisenberg uncertainty principle

What is the significance of the quantity 4π in the Heisenberg uncertainty principle? $Δp \times Δx = \frac{h}{4π}$ The focus of the question is to learn why the ratio of a circle's circumference to ...