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)

1
vote
1answer
33 views

Atomic number $Z$

If electrons were spin-$\frac {3}{2}$ instead of spin-$\frac {1}{2}$ , what would be the atomic number $Z$ for the first noble gas ?
3
votes
2answers
36 views

Gaussian Convergence Issue for N2+N PES

I am trying to obtain a potential energy surface (PES) for $\ce{N2 + N}$ combination using scan feature of Gaussian. I have tried different combinations of basis ...
3
votes
0answers
19 views

How to visualize or think about spin waves (magnons)?

According to Wikipedia: "A magnon is a quasiparticle, a collective excitation of the electrons' spin structure in a crystal lattice." I have little pictures in my mind for other quasiparticles. For ...
2
votes
1answer
128 views

Usefulness of the outdated Bohr model?

Whilst the Bohr model is incomplete and incorrect, it had limited usage in predicting spectral lines. In the same way, could it possibly with limited accuracy, be used to predict the outcome of ...
10
votes
2answers
185 views

How to find the second order perturbation to wave function?

Today, I'm looking for how to find the 2nd perturbation to the base in Rayleigh Schrödinger Perturbation Theory (RSPT). SETUP Starting from the 2nd order perturbation in Dirac's notation: ...
0
votes
0answers
28 views

Quantum Numbers and Ions

How do quantum numbers change for ions? A sample question: Give the set of four quantum numbers that could represent the electron lost to form the Rb ION from the Rb atom. The answer given is n=5; ...
1
vote
1answer
24 views

Ignoring spin, consider an electron in a hydrogen 2p orbital, what is its orbital magnetic moment?

I know that a magnetic dipole moment is given by $$\mu=\frac {-e}{2m}I$$ and that the z component of angular momentum is $$m_j\hbar.$$ However, I have also seen that angular momentum $I$ is given by ...
5
votes
1answer
328 views

Why are so many wave functions associated with hydrogen?

According to Wikipedia, there's an infinite set of possible wavefunctions (orbitals) for the hydrogen atom: $$\psi_{n\ell m}(r,\theta,\phi) = \sqrt {{\left ( \frac{2}{n a_0} \right ...
4
votes
0answers
48 views

Abnormal termination of GAMESS in frequencies calculation

I want to optimize geometry and to analyse frequencies for transition metals ($\ce{Cu}$, $\ce{Mn}$, etc.) compounds using GAMESS. I use Avogadro for preparing input files and I have a problem: one of ...
5
votes
1answer
48 views

Do core electrons in bulk material have discrete energy levels or continuous energy band?

The energy band of valence electrons gets smaller and smaller when the lattice (bulk) atoms are more and more separated from each other, until discrete energy levels are formed, due to the isolation ...
0
votes
2answers
66 views

Heisenberg's Uncertainty Principle's inequality [closed]

In the uncertainty principle , whats the significance of the inequality sign ? Why is it not equal to over there ? Why do we say greater than equal to instead of just equal to ?
0
votes
0answers
23 views

Is there any reason why we use a certain method rather than a possible one to find the needed?

I encountered a problem which used the equation E=hv to find out the frequency from a given wavelength but what if we used the simple equation c=frequencyXwavelength immediately. Hint: I tried to ...
0
votes
0answers
17 views

Correlation between crystal structure and underlying atomic properties

Can the crystal structure of an element/metal be explained by any underlying atomic or quantum mechanical properties of the element or is it an intrinsic property by itself (like atomic number)?
4
votes
1answer
56 views

Please explain the following graph for a quantum mechanical harmonic oscillator

Graphs such as the above keep coming up when talking about harmonic oscillators in a quantum mechanical sense. However, I simply cannot make sense of them. What does each line represent why are they ...
4
votes
1answer
52 views

What is an orbital boundary surface?

Could anybody explain the following statement: "The boundary surface is a common way to represent atomic orbitals, incorporating the volume in which there is about a 90 percent probability of finding ...
-1
votes
1answer
35 views

when do we indicate the “+ or -” sign in uncertainty [closed]

how can we know when to indicate "+ or -" sign in uncertainty calculations because I noticed some problems has been solved by this sign and some has not.
9
votes
1answer
169 views

Is there a general / simple formula for Slater's rules?

I just learned how Slater's rules work on Wikipedia. These rules really are very simple. But the presentation of the rules seemed not very efficient. I would think there would be someway to set up and ...
2
votes
1answer
37 views

Show that there can be 18 electrons in a “g” subshell

I'm learning about quantum numbers right now, and I can't figure out how to calculate the number of electrons in each shell without memorizing it. Is there a formula to find the possible numbers of ...
2
votes
1answer
80 views

How can you manage SCF convergence problems?

"Failure to locate stationary point, SCF has not coverged" This is the most annoying message after Optimization run ( even with a good primary start geometry like UFF we ay see that) . The only ...
5
votes
1answer
117 views

Do multielectron atoms have nodes?

For hydrogen, other than in the 1s state, the electron wavefunctions have radial and/or angular nodes where the electron probability density is zero. In helium or further atoms with more than one ...
1
vote
0answers
31 views

What's the relation between the octet rule and quantum exclusion and how is it related to oxidation state?

What in the quantum nature of electrons gives rise to the octet rule? How is it related to the fact that an element cannot have an oxidation state higher/lower than the complementary to 8?
0
votes
0answers
21 views

Calculating the angular momentum for these orbitals

Here is the question: I got through part a (with 1, -1, 0, and 0), but I'm stuck for part b. I looked up the radial and spherical harmonic wavefunctions for $n, l, m_l$ = 211 ; and I figure since ...
2
votes
1answer
42 views

HOMO and LUMOs of Carbon based Compounds

Why are the HOMO and LUMOs often $\pi$ orbitals in carbon based compounds that contain multiple double bonds or conjugation such as ethene and butadiene?
2
votes
1answer
156 views

How to Run GAMESS and Avogadro on Command Line?

I always use GAMESS and Avogadro on my own laptop. Recently I installed them on our university supercomputer and started using them by remote logging-in. On the laptop everything was super easy but ...
4
votes
1answer
80 views

Post-Hartree Fock Methods

I'm new to computational chemistry, so perhaps this question has an obvious answer. I'm wondering what the intuitive reason for constructing Slater determinants that involve excited states is, when ...
8
votes
2answers
106 views

What is the meaning of “no Hessian Eigenvalue ”?

When running GAMESS for finding Hessian Eigenvalues and frequencies ( using Optimization with hessian calculation at the end ) , I have seen there are times that it comes out "without any ...
2
votes
1answer
31 views

Why doesn't the atomic number change by two in the process of production of Americium?

Looking at the bomardment of uranium-238 this is what I see. First, I see a uranium-238 atom with 92 protons bombarded with a neutron. The neutron then undergoes beta decay into a proton. So we ...
1
vote
0answers
57 views

What is Barrier-less reaction in Quantum Chemistry?

After finding a reaction "Transitional State " by GAMESS and finding Hessian Eigenvalues, my project instructor said: " seems your imaginary frequency ( negative eigenvalue ) is not that big ( it is ...
1
vote
2answers
33 views

Where to find pre-optimized files for Quantum Chemistry Softwares?

Many times Geometry optimization gets very time consuming ( even with access to super-computers ). I have seen some pre-optimized libraries for biomolecules like proteins that you can easily download ...
0
votes
1answer
40 views

the particle in 1-D box momentum and total energy(P.E + K.E (x))

Employing the particle in 1-D box can momentum and total energy(P.E + K.E (x)) can be measured simultaneously?
0
votes
0answers
38 views

How do you Calculate the Work Function for the Ejection of an Electron

The question is: Below is a photoelectron spectrum of the $\ce{N2}$ molecule. The spectrum was taken from an experiment in which photons of " $= 2.4825~~nm$ were fired at gaseous $\ce{N2}$. ...
1
vote
2answers
65 views

Is probability of finding electron changing here?

We all know what is a wave function. There is a technique to convert non normalized wave function to normalized wave function. In case of non normalized wave function integration of square of wave ...
7
votes
3answers
1k views

Temperature of an atom

I read somewhere that the temperature of an atom is not defined. The definition of temperature is only for larger systems. Why is this so?
5
votes
1answer
94 views

Why neutrons are neutral?

If electrons have a negative charge and protons have a positive charge then how come neutrons have zero charge without consisting of protons and electrons ? (Excuse my bad English)
4
votes
3answers
114 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 ...
3
votes
1answer
85 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 ...
3
votes
1answer
248 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 ...
3
votes
1answer
48 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
152 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
64 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
82 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
98 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
65 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
72 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
54 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
52 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 ...
4
votes
2answers
94 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
41 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
196 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
29 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 ...