Theoretical Chemistry

The use of mathematical and computational methods to build theories explaining observations of chemical reactions, such as quantum chemistry. | Contact experts in Theoretical Chemistry to get answers

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Questions related to Theoretical Chemistry

Should the normal mode of vibration leading to the transition state be removed?

I would like to know whether the normal mode of vibration of the reactant should be deleted when calculating $\Delta ZPE$ and $\delta G_{\text{corr}}(T)$, where $\Delta ZPE$ is the zero-point...

05 May 2017 9,623 5 View

Basic question of HF vs Hybrid DFT.

A rather basic question just to make sure I understand some of the theory. I have an amino acid backbone, with the amine and carboxyl groups positively and negatively charged, respectively...

05 May 2017 8,518 15 View

For an equilibrium calculation, which one should be taken as the dissociation reaction of HO2? O2+0.5H2-->HO2 or O2 +H-->HO2 or O+OH-->HO2? Why?

For an equilibrium calculation, which one should be taken as the dissociation reaction of HO2? O2+0.5H2-->HO2 or O2 +H-->HO2 or O+OH-->HO2? Additionally, I see some reearchers took...

05 May 2017 3,297 14 View

What is the needful command or solution to be applied for the frequency calculation job failure using Dmol3?

Erorr displayed in the output file! Message: Entering vibrations sectionHarmonic frequencies will be computed by finite differences. Number of displacements per atom is: 2 Step size for finite...

05 May 2017 8,882 0 View

How to calculate the frequencies from the force constant matrix in Cartesian coordinates (Gaussian)?

I would like to determine the frequencies of the normal modes from the force constant matrix printed as "Force constant in Cartesian coordinates" in the Gaussian .log file. How to perform it? Are...

05 May 2017 5,821 3 View

How could we differentiate between sigma and pi molecular orbitals?

05 May 2017 4,587 3 View

Which baisis set is good for telleurium compond for dft calculation ?

I want to do optimization in DFT for tellurium containing organic compound. I have used def family basis set and even basis set 3-21* and land2dz basis set. Please suggest some suitable or basis...

05 May 2017 3,395 7 View

How to extract force constants from the Gaussian .log file?

I would like to get Force constant matrix calculated using iop(7/33=1) from the Gaussian .log file. I guess that they are placed into the last block, perhaps after the NImag=n data. Is it true? If...

05 May 2017 5,387 15 View

How can I calculate the anisotropic magnetic susceptibility of a molecule?

I would like to calculate the anisotropic susceptibility of certain molecules, that is, I would like to know how the magnetic susceptibility of the molecule changes as a function of orientation...

05 May 2017 6,146 5 View

How to calculate Second Order Hyperpolarizability (Gamma) both for static and frequency dependent using Gaussian 09?

I have used following keyword in the route section "polar=(DCSHG,Cubic) CPHF=RdFreq" and frequency 0.0428 a.u. In the output I have obtained alpha and beta values but how can I obtained gamma...

05 May 2017 7,351 8 View

How to compute multiple excited state dipolemoments in one TD job?

Hi, I am working on a molecule of 34 atoms trying to compute excited state dipole moment using density=all. I know I can choose a state of interest by using root keywork (root=3 for third...

05 May 2017 4,676 3 View

What are the advantages of the analytical solutions offered by Hartree-Fock over grid-based integration of DFT in context of large system computation?

I want to know how the analytical solutions of Hartree-Fock can come handy during computation of large systems although the formal scaling order of HF is N^4 compared to N^3 scaling of DFT (where...

05 May 2017 1,231 3 View

How shall I find or calculate the Gibb's free energy for a typical molecule as well as transition state from Spartan 14 wavefunction?

Hello everyone, I am using Spartan 14 wave function to calculate Gibb's free energy of a particular molecule as well as the transition state. But unfortunately, I am a bit unknown of how to use or...

05 May 2017 6,502 2 View

Gaussian log file is not printing anything as calculations are running in the background?

Dears I am doing QM/MM calculations and trying to optimize a Gaussian input file of about 35000 atoms. But output.log is not printing anything except coordinates even Gaussian calculations are...

05 May 2017 1,864 6 View

Is there any tool for determining functional groups in a given compound?

I'm looking for a tool that can give how many methyl groups, hydroxyl groups etc. are in a compound from it's SMILES, SDF or MOL2 format.

05 May 2017 9,876 5 View

Can anyone help me on how to get coordinates of cardanol (C21H36O)?

I want to create input file of cardanol (C21H36O) and compute some properties in GAMESS software. The coordinates of C21H36O are required in the input file. I have tried to check in chemspider but...

05 May 2017 1,843 3 View

I am trying to calculate absorption spectra using tddft but it is giving lambdamax=320nm but exp = 410 nm

I am using tddft on optimized geometry [ #p cam-b3lyp/6-31g* td=(singlets,nstates=10) pop=full gfprint gfinput fchk ]. I am getting Excited State 1: Singlet-A 3.8727 eV 320.15 nm f=0.1523...

05 May 2017 3,114 15 View

How to analyze the charge density in CHG file generated by first principle molecular dynamics?

Hello, researchers. I'm now studying on the reactions between Al and Fe2O3 by first principle molecular dynamics. I have got the CHG file, then, how to export and display the charge density at...

05 May 2017 8,097 2 View

Difference between one-electron orbitals in Slater determinant and the basis set

Hi, I have pretty much basic question related to ab-initio HF method: What is the difference between one-electron spin orbitals we use in Slater determinant and the basis set functions? What is...

05 May 2017 4,557 9 View

How can I overcome negative frequencies that occur during Gaussian calculations?

How can I overcome negative frequencies that occur during Gaussian calculations?. I elongated my atomic positions along the normal coordinates of my imaginary frequency. You see "quer-rc.out"...

05 May 2017 6,496 6 View

I am trying to optmize a reaction complex but run always breaks. what should I do?

I am trying to optimize a reaction complex in which CH2NH is absorbed in water ice and then CH2 attack on one of its H- atom. now when I try to optimize it, the optimization profile remain nearly...

05 May 2017 5,372 14 View

How do we calculate atomic spin density using Molpro?

I want to calculate CASSCF/CC-PVDZ for C4 molecule in triplet state. Thus I want to know the spin density of each atom.

05 May 2017 8,097 2 View

How to calculate reorganization energy for hole/electron in Gaussian software?

I am looking the appropriate keyword and how to do that calculation in that software. Really, I do not understand that following what all that they mean. what do neutral energy of optimized...

05 May 2017 9,099 2 View

Chemistry experts - what is the correct and official notation of hydroxyl radicals?

Over the internet I have seen the following ways it was written: OH (no dot) OH. (dot in subscript position) ·OH (middle dot before OH) OH· (middle dot after OH) OH· (dot in superscript position,...

05 May 2017 8,836 3 View

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