Questions tagged [quantum-chemistry]

Quantum chemistry is a subfield of quantum mechanics. Like its parent field, quantum chemistry focuses on understanding physical phenomena occuring at the atomic scale. Quantum chemistry however is more focused on providing useful descriptions of electronic structure to aid in understanding chemical problems (e.g. reactions, spectra, dynamics, ...).

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Electron Spin, and the Stern-Gerlach Experiment

I think I understand the basics of the electron spin. However, I'm trying to figure out how to tell if, when shooting a beam of atoms (the Stern-Gerlach experiment), how to tell if an element will ...
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36 views

How can I obtain the wave function of the dihydrogen system, by hand using Self Consistent Field DFT calculations? [duplicate]

After doing some energy calculations for the $\ce{H2}$ system in Gaussian, using ωB97X-D/STO-3G level of theory, and generating a .wfn file, I wanted to understand better how the computer does ...
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145 views

What is meaning of LAV2P basis set?

I am working on energy optimization of molecular structure using DFT with Schrödinger software and I found that job is running on LAV2P basis set. I want to know what is the meaning of this basis set ...
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47 views

Ionization energy and charge localization: π-bonds/systems and ionization energy

Page 35 of my textbook, Mass Spectrometry by Jürgen H. Gross, says the following in a section on ionization energy (IE) and charge localization: Molecules with π-bonds have lower IEs than those ...
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162 views

Does the radius of the atom change when an electron is excited?

The radius of the atom increases when the electron in a hydrogen atom undergoes a transition from the 1s-orbital to a 2p-orbital. How is this possible? Why does exciting an electron to a higher ...
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56 views

Getting radial Kohn-Sham orbital from the output of an electronic structure code using gaussian basis sets

As we know that in solving the Schrodinger equation (Kohn-Sham equation), we expand the wavefunction in terms of some basis sets and them optimize the energy (the expectation value of Hamiltonian) by ...
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108 views

What is the significance of antinode at r=0 in the plot of radial wave functions of s-orbitals?

Why should there be an antinode at r=0? I can comprehend the presence of node at r=0 for p,d,f orbitals; but I don't understand that of s-orbital. Is there any intuitive approach?
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47 views

Is it possible to calculate electrostatic interactions using QM methods?

I'm trying to calculate an accurate electrostatic repulsion (and possibly attraction) energy term for various small molecules, using Quantum Mechanics (QM) methods. These may include molecules such as ...
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35 views

Potential energy curve for dissociation of cation of carbon dioxide

Can anyone suggest me some literature where I can find the potential energy curve or the electronic states for singly ionized $\ce{CO2}$ ($\ce{CO2+}$) dissociating into singly charged oxygen ($\ce{O+}$...
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47 views

Photoelectric effect — Expected observations for waves

I understand why treating light as particle-like photon packets leads to the observed results. I seek to understand why one would expect different results if light were treated as a wave (and thus ...
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76 views

Can the oxidation of hydrogen peroxide be reversed? [closed]

Hydrogen peroxide is said to be unstable, for it undergoes auto-oxidation on standing/heating: $$\ce{2H_2O_2 -> 2H_2O + O_2}$$ where $\Delta S=\pu{70.5 J {mol}^{-1}K^{-1}}$ and $\Delta H^{\Theta} ...
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Significance of this unusual matrix element

Recently, I was solving some questions on Rigid Rotor. I found this question very amusing. Evaluate the integral i) <$Y_{l,m+2}$ | $L_{x}^{2}$ | $Y_{l,m}$ > I evaluated it, found that the value ...
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197 views

Why do we neglect the zero point energy in statistical mechanics?

Quantisation associated with translational modes can be modelled like a particle in a box (PiB). $$E_n = \frac{n^2h^2}{8mL^2} \qquad n \in \mathbb{Z} \, | \, n \ge 1$$ By the equation above, the ...
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Scan type of DFT calculations adding Freq=Raman keyword [duplicate]

I´m doing a scan calculation by adding Freq=Raman keyword. My objective is to obtain the Raman spectrum of each conformation in my compound. However, when i write the Freq=Raman Keyword, only the ...
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259 views

Is OH + CO → CO2 + H an elementary reaction?

Is $$\rm OH + CO \longrightarrow CO_2 + H$$ an elementary reaction? How could I tell? I could break the reaction into $$\rm OH\ (+ M) \longrightarrow O + H\ (+ M)$$ $$\rm CO + O \longrightarrow ...
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845 views

Why does q/m ratio(specific charge) depend on nature of gas in anode ray experiment?

I can't understand why $q/m$ ratio changes in anode ray experiment (discharge tube experiment) (which was carried out by Goldstein) with change in nature of gas? Since $q=1.6\times10^{-19}\ \mathrm C$...
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59 views

Schrödinger's equation [duplicate]

Schrodinger's equation has been successfully solved in one-electronic systems, such as the ionic molecular hydrogen $\ce{H2+}$. What is the exact reason that this equation can not be applied for ...
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20 views

Filling up of electrons [duplicate]

Is it necessary that filling up orbitals start from spin-up orientation only? And also, is it mandatory to fill the electrons with one kind of spin or they can be filled with spin up and spin down(as ...
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48 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 ...
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1answer
1k 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?
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$\psi$ Represents amplitude of electron wave and $\psi^2$ represents electron density in a given space. How?

The $\psi$ represents amplitude of electron wave. So it's dimension should be $\left[L\right] $. But $\psi^2$ represents density of electrons in a given space. So it's dimension should be $\left[ML^{-...
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3k 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?
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1answer
75 views

Can carbon have electrons in a 5d orbital? [closed]

(a) Sketch the radial probability distribution for a 5d orbital in a carbon atom. You should label the axes, but do not need to include numbers. Use arrows to indicate the radial nodes. (b) Label the ...
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1answer
145 views

Why is the volume related to the probability of finding an electron? [closed]

thank you for your time. I was wondering about the correlation between volume and probability of finding an electron. we know that if we move away from the nucleus, we are going to get less ...
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1answer
180 views

Quantum Chemistry, quantum physics [closed]

In both classical and quantum mechanics knowledge of the present state of an isolated system allows it's future state to be calculated. If yes then why if not then why ?
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195 views

Band gap of Transition Metal Dichalcogenides

What phenomena is responsible for the shift of the nature of the band gap of transition metal dichalcogenides from being indirect band gaps to direct band gap material once it is slimmed down from ...
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1answer
716 views

Potential energy of electron in excited hydrogen atom

The angular momentum of electron in an excited H atom is $\frac{h}{\pi}$. The potential energy (PE) of electron is? Let $\frac{h}{\pi}=\frac{nh}{2\pi}$, therefore $n=2$. So, $$E=\frac{-13.6}{4}=\pu{-...
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552 views

Explain!“An orbital of smaller size means there is more chance of finding an electron near the nucleus” [closed]

how can orbital of smaller size increase the probability of finding the electron near the nucleus Please explain in simple language.
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1answer
52 views

How to find the number of valence electrons with the help pf quantum numbers? [closed]

I'm bit confused on how to find the number of valence electrons. For example, Boron ($\ce{B) has the electronic configuration as: $\mathrm{1s^2 2s^2 2p^1}$. So what would be its number of valence ...
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1answer
38 views

Absorbance maxima of polyenes [closed]

Can anyone tell me how to approach this question from USNCO 2013?
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1answer
37 views

What is the velocity of de Broglie wave?

Here is my calculation: note: $ν$ – frequency, $V$ – velocity of wave, $v'$– velocity of object. $$ \begin{align} λ &= h/mv' \tag{1}\\ mc^2/h &= ν \tag{2}\\ λν &= V \quad \text{(wave ...
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1answer
54 views

Quantum Chemistry [closed]

How to find the degeneracy of a given state in quantum mechanics? What is the formula?
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1answer
81 views

What does orbital mean, exactly? [duplicate]

My teacher told me that orbital is the probability distribution data of the electron around nucleus which is amplitude data in a way. An example of how my teacher actually told what it means involves ...
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1answer
136 views

How is it that the Inner Periodic Table Sections (have 15 elements each) versus their f-block (with only 14 element’s electrons each)? [closed]

Given: 1. the “Lanthanide and Actinide” Inner Periodic Table Sections (each have 15 elements) versus the f-block Orbitals (which only have a capacity for 14 out of the 15 element’s electrons each) - ...
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1answer
300 views

Schrödinger wave function for 3s orbital of hydrogen atom [closed]

I am unable to understand what these terms in the wave function represent and how to solve it. For 3s orbital of hydrogen atom, the normalised wave function is $$Ψ_\mathrm{3s} = \frac{1}{81\sqrt{3π}}\...
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1answer
57 views

Chemical reaction energy barrier width [closed]

Well chemistry before the discovery of quantum world was saying:"In order for a chemical reaction to happen , reactants must have enough energy to be converted into products."I was wondering now that ...
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1answer
242 views

How to give different Basis set to different atoms in molecules using GAMESS-US [closed]

I am new to GAMESS-US, I am trying to do UHF for DyC10H10 while giving different basis set to Dy, C, H to reduce the computational cast. Until I tried with following input using manual. OUTPUT *** ...
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1answer
191 views

What happens if the electron in the lowest energy level of an atom loses its energy?

What happens if the electron in the lowest energy level of an atom loses its energy? Excited states spontaneously give of energy and transition to a lower energy state. Why can't an electron in the ...
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1answer
288 views

What is the difference between carbon in an excited state and with sp³ hybridization?

What is the difference between the carbon in the excited state, $\ce{[(1s)^2] (2s)^1 (2p)^3}$, and $\pu{sp^3}$ hybridization?
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1answer
175 views

Is there a fixed corresponding orbital for every specific magnetic quantum number? [duplicate]

Does each value of $m$ have a fixed orbital (given the value of $l$ as well as $n$)? For example, if I know that $n = 2$, $l = 1$, and $m = -1$, which orbital ($\ce{p_x}$, $\ce{p_y}$ or $\ce{p_z}$) ...
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1answer
32 views

how electron can go towards nucleus and then go far apart from it as in p orbital?see discription

In p orbital shape is dumbbell shaped which means electron go in the shape of dumbbell means first towards nucleus then go away from it. How can be this possible because first electron is attracted ...
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1answer
96 views

From a Quantum Chemistry Point of View how can I break Bonds without Heating?

Is it possible to dissolve/break bonds using strong alternating magnetic fields at high frequency? (Perhaps from tesla coils?) Could you use resonance to cause the bond to weaken over time? If so how ...
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1answer
40 views

Help understanding the equation for Spin Energy in Zero Field

I’m working with a system that experiences spin frustration and for me this is the first time dealing with such a phenomenon. To grasp the concept, I’ve decided to go to the basics and read the ...
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2answers
62 views

Why is the first affinity energy negative?

So, I've found a number of somewhat obscure responses to this question but I'm looking for something concrete: Why is the first affinity energy negative for most elements? I appreciate that this is ...
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1answer
145 views

if the shared electrons in covalent bond revolves around their nucleus, how they hold the two molecules together? [duplicate]

Covalent bonds are formed by sharing electrons. The pictures depicting this bond make it seem like that the shared electrons stay in a fixed/limited place. What happens in reality? If they rotate ...
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1answer
601 views

what is meant by stability and potential energy of molecules in cases of formation of bonds?

molecules form chemical bonds in order to gain stability. it is said that forming bonds leads to lower potential energy of molecules and makes them stable. what does stability mean? how formation of ...
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2answers
608 views

What is the magnetic quantum number -1 vs +1?

In my book it states the magnetic quantum number “$m_\ell$" is the spatial orientation of the orbital with respect to a standard set of coordinates. I get what $n$ and $\ell$ is, but what does it mean ...
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2answers
121 views

Electron tunneling between orbitals

Electrons can move through potential barriers by tunneling. Atomic/molecular orbitals are separated by energy differences. Therefore I was wondering if an electron can tunnel from one orbital to ...
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2answers
129 views

Are the electrons in an atom always 'locked' with their proton?

Suppose you have a single atom, say carbon, carbon has six electrons, and six protons. Now is there anything associating the six protons locking the six electrons other than coulombic forces? When we ...
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1answer
56 views

What is the physical significance of the fact that spin operators do not commute? [closed]

So we looked at the Stern-Gerlach experiment and I understand the basic principle; when a stream of silver atoms is passed through an inhomogeneous magnetic field, and the Ag atoms are deflected ...