The tag has no wiki summary.

learn more… | top users | synonyms

1
vote
1answer
38 views

Why is the 8-electron rule more important than the 2- or 18-electron rule

Why is the fulfilled electronic configuration of only $p$ orbital is stable. I mean why $II-B $ group with fulfilled $d$ orbital,$II-A$ group with fulfilled $s$ orbital...are not stable. Why makes ...
2
votes
1answer
43 views

Animate molecular vibrations as multiple xyz coordinate files

I have a frequency calculation by Gaussian09. Now I would like to extract vibrational modes as a set of xyz coordinate files. I would like to manually recompute numerically the points along a ...
0
votes
2answers
52 views

Degenerate Orbitals

How do I know if an atom has degenerate orbitals? My Understanding I understand that degenerate orbitals mean orbitals that have the same energy level for the same n. However, how do I distinguish ...
1
vote
1answer
47 views

Bonding, multiplicity and quantum chemistry for FeP$_2$

I'm trying to do some quantum chemical calculations for the linear molecule FeP$_2$ in the gas phase as well as its crystal (orthorhombic symmetry like here). I am lead to believe that in both cases ...
1
vote
0answers
33 views

Are multiple transition states possible? Criteria to choose the correct one?

I am studying a reaction using electronic structure methods using various software packages (ORCA,GAMESS, G09) and have found two possible transition structures between product and reactant. Both have ...
1
vote
0answers
57 views

Which of the following statements is not true about quantum theory? [closed]

Which of the following statements is not true of quantum theory: A: Light energy from an object is emitted in small packets called quanta. B: The Bohr atom is quantized with the electrons ...
3
votes
1answer
69 views

What does the subscript of atomic orbital mean?

As everyone knows, the atomic orbital can be classified as $s, p_z, p_x, p_y, d_{z^2},d_{xz},d_{yz},d_{xy},d_{x^2-y^2}$ and so on. I want to know the meaning of $z^2,x^2-y^2$ and so on. Maybe this is ...
4
votes
3answers
182 views

Does partial charge violate the law of quantization of charge?

Well, we know that charge is quantized. Quoting wikipedia below, Charge quantization is the principle that the charge of any object is an integer multiple of the elementary charge. And we know ...
2
votes
0answers
47 views

Why is the orbital angular momentum of a pi electron along the axis of two atoms' molecule one?

I'm reading quantum chemistry. The book says that the orbital angular momentum of a $\pi$ electron along the symmetry axis of a molecule made up of two atoms is $\pm 1$. I think this is a primary ...
7
votes
4answers
897 views

Why is the alpha particle called a particle when it is made of four particles?

We know the alpha particle is the nucleus of helium. It contains four subatomic particles - two protons and two neutrons. The protons and neutrons are further made of particles called up and down ...
3
votes
2answers
178 views

The energy gap between a pi-conjugated system with (2 bonding and 1 anti-bonding orbital) and (1 bonding and 2 anti-bonding) orbitals

I asked a question previously about "why" it is the case the expanding the size of pi-conjugated systems decreases the required energy to excite an electron from a HOMO to a LUMO band: Why does the ...
5
votes
3answers
278 views

Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?

Quoting from this site: As conjugated pi systems become larger, the energy gap for a π - π* transition becomes increasingly narrow, and the wavelength of light absorbed correspondingly becomes ...
4
votes
1answer
132 views

Why are excited Slater determinants used to describe electron correlation?

Usually the first step in describing the electronic wave function of a molecule or atom is to describe it with a single Slater determinant. I get that this is an independent particle approximation, ...
2
votes
2answers
73 views

How to properly denote imaginary magnitudes of vibrational frequencies

Vibrational frequency computations provide the magnitudes of vibrational frequencies for each vibrational mode of a molecule ($3N-6$ degrees of freedom for non-linear molecules and $3N-5$ for linear ...
-1
votes
1answer
62 views

Quantum Chemistry: For what value of n (principal quantum number) will the expectation value of the radius equal to one-half of a 100 Å box size? [closed]

A hydrogen atom is in cubical box with side lengths equal to 100 Å. For what value of n (principal quantum number) will the expectation value of the radius equal to one-half the box size?
2
votes
2answers
64 views

Defining and testing custom made DFT functionals?

What is a good and free software for this endeavor? Any recommended articles on the subject? I want to design dft functionals, trying out different parametrizations and optimizing mixing constants for ...
4
votes
1answer
137 views

Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable ...
0
votes
0answers
45 views

Do these compounds Na$_x$IrO$_2$ and NaOsO$_2$ exist?

Based on some physics background, I want to know whether have we synthesized these two materials: $\ce{Na_{x}IrO2}$ and $\ce{NaOsO2}$ in the lab, if so, what properties do they have? I will be very ...
1
vote
2answers
75 views

Quantum chemistry: CCSD(T) with aug-cc-pVTZ on omeprazol

I know that CCSD(T) with aug-cc-pVTZ basis set for geometry optimization of omeprazol, i.e. the active substance in Losec is not suitable using the normal computers. The substance is: omprazol Can ...
0
votes
1answer
313 views

Why are wave functions orthogonal?

It seems that all wave functions studied in physical chemistry are orthogonal (e.g. particle in a box, hydrogen atomic orbitals). Does this come about because we purposefully make them orthogonal, or ...
3
votes
1answer
98 views

Bonding and nodes with molecular orbitals

If there is more overlap of the same sign wave function, this apparently leads to less energy. However, I don't understand why. My professor said that there would be less nodes, and less nodes means ...
1
vote
0answers
41 views

An alternative basis set for analytical computation of two electron integrals

It is well known that the usage of the Gaussian basis set, in contrast to Slater basis set, leads relative simple semi-analytical expressions for the two electron repulsion integral $(ab|cd)$. Could ...
2
votes
0answers
98 views

Magnetic moment of coordination complexes?

To understand the commonly quoted magnetic values of coordination complexes (central ion) we use $$m_l=\sqrt{n(n+2)} \text{BM where BM}=\frac{e\hbar}{2m_e}\text{JT}^{-1}$$ $n$=number of unpaired ...
2
votes
1answer
82 views

How can we write the wave function in quantum mechanics?

In quantum mechanics, while writing the wave functions we can take a product of the spatial and the spin parts.But what does it means? What is the meaning of the spatial wave function and the spin ...
3
votes
1answer
538 views

Does hydrogen peroxide exhibit intramolecular hydrogen bonding interactions?

We know that intermolecular Hydrogen bonding is seen in Hydrogen peroxide $(H_2O_2)$.But is intramolecular H-bonding,i.e. Hydrogen bond between an oxygen atom and a hydrogen atom attached to the ...
4
votes
1answer
119 views

Why are the total energies of transition states so commonly corrected for zero-point vibrational energy?

So often I see total energies of transition states corrected for zero-point vibrational energy which always confuses me. Zero point energy is the lowest energy that a ground state molecule can have ...
6
votes
2answers
105 views

How can enzyme/substrate reactions that adhere (largely) to quantum theory also require 'Newtonian' consideration of gravity?

I'd just like to ask for a little clarification here due to confusion from interdisciplinary studies. I'm currently reading the 1976 paper related to the recent 2013 Nobel Prize for Chemistry, by 2 ...
0
votes
0answers
20 views

What is the difference between ZCT Tunneling correction and Wigner Tunnelig correction in computational Quantum Chemistry?

I've been doing some computational calculations about kinect rates of a reaction and I was told to perform both ZCT and Wigner corrections to calculate these rates. But I don't know the difference ...
9
votes
1answer
139 views

Derivation of the Hartree-Fock equations. Functional variation

I would like to ask a question about mathematical derivation of the HF equations. Some moments related to the functional variation are not clear for me. I read a book of Szabo and Ostlund "Modern ...
2
votes
1answer
372 views

Calculating the probability of finding an electron between $0.25L$ and $0.75L$ in “particle in a box problem”

If the wavefunction of the electron in a box of length L is $$\psi{(x)}=\sqrt{\frac{2}{L}}\cdot\sin{\frac{n\pi x}{L}}$$ What would be the probability of finding the electron between $0.25L$ and ...
2
votes
1answer
56 views

Gaussian vs ABINIT for solids

I see that Gaussian has feature to set periodic boundary conditions specifying the parameter Tv in the input file. Does it do it via the plane wave basis set? Also, the question is whether it is ...
1
vote
1answer
154 views

The ionization energy of $\ce{H2^+}$ molecule ion

I am trying to compute the ionization energy of $H_2^+$ molecule ion from the electronic energy spectrum. The question is whether one should use the purely electronic Hamiltonian or the Hamiltonian ...
3
votes
2answers
135 views

Which computational method/basis set should I use for small molecular ions?

I apologize for a perhaps newbie question. I would like to compute the potential energy surface for several small molecular ions, like $\ce{H2+}$ and $\ce{H3+}$, using quantum chemistry software. ...
3
votes
1answer
69 views

Special electron configurations in p block on periodic table?

Gold and Chromium have weird electron configurations, because electrons are differently divided : eg an electron jumps from a s-orbital to a d-orbital to have a half-filled s orbital and a fully/half ...
5
votes
2answers
127 views

Have we ever created artificial metals?

I really don't know anything about chemistry, but I was wondering about the following vague question: has any substance been created that does not contain any metallic elements, but is metallic? In ...
2
votes
2answers
112 views

CI without Hartree-Fock SCF

Usually textbooks on CI takes the SCF Hartree-Fock orbitals as a starting point. Can one use the configuration interaction method starting directly from the single-particle Slater determinants ...
2
votes
1answer
295 views

Degeneracy of orbitals?

Why is that in an external magnetic field(uniform) the degeneracy of d,f orbitals is lost but the degeneracy of p orbitals remain intact if the main cause of losing degeneracy is the difference in ...
3
votes
2answers
181 views

Approximation of electron density of a small molecule

Starting point for Quantum Theory of Atoms in Molecules (AIM) is the electron density $\rho(r)$. It could be determined experimentally (X-ray diffractions). I want to know how can we estimate them ab ...
15
votes
4answers
469 views

How can antibonding orbitals be more antibonding than bonding orbitals are bonding?

In molecular orbital theory, the fact that a bonding and antibonding molecular orbital pair have different energies is accompanied by the fact that the energy by which the bonding is lowered is less ...
3
votes
1answer
50 views

Database for molecular dipole transition moments?

I'm looking for the dipole transition matrix elements for electronic transitions between the ground and excited states of the carbon dioxide cation, $\text{CO}_2^+$, that is, objects like ...
3
votes
1answer
396 views

Quantum dot band gap energy equation

I have been looking into certain approximations for band gap energies in quantum dots and have found this paper (Band-structure-corrected local density approximation study of semiconductor quantum ...
2
votes
1answer
188 views

Intrinsic Reaction Coordinate - What does 'Connectivity' really mean?

I am currently in the process of connecting transition state (TS) structures to other minima in order to determine a reaction pathway. Now I understand the basic concepts of this method. You start ...
4
votes
2answers
329 views

Why are these molecular orbitals invalid for hexatriene?

Here are the MOs (more accurately, the breakdown of the MOs) for conjugated hexatriene: Now, when first asked to draw the MOs myself, I drew this one for $\psi_3$: It still has two nodes, and is ...
8
votes
1answer
239 views

Naming of quantum chemistry basis sets

For some DFT calculations I performed with localized (Gaussian) basis sets, I wonder how the basis sets I used are properly named. The names I could gather are: H, C and O: 6-311G(d,p) Al: 8-511G* ...
19
votes
7answers
15k views

Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus?

My chemistry book explains that even though electrons in the 2p orbital are closer to the nucleus on average, electrons from the 2s orbital spend a very short time very close to the nucleus ...