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

Which result is moreliable: AIM or NBO?

I have done the AIM and NBO analysis for a complex system of two identical molecules to check the HB between them. there are some differences between the AIM and NBO results. I can see bond a...

06 June 2017 1,126 7 View

PES for charged system

I want to scan potential energy surface for ((CH3+) + O2) reaction, but when I am trying to scan from 3.0 to 1.5A distance the spin as well as charge is also changing at the same time. How can I...

06 June 2017 4,808 2 View

How to obtain minimum energy paths from reactant to two different products via single transition state?

Hello, The system that we currently working seems to involve the formation of two different products via a common transition state. Recently this kind of scenario where the reaction involves the...

06 June 2017 5,633 5 View

Rocbs Convergence failure Error termination via Lnk1e in /home/g09/g09/l502.exe

#P ROCCSD(T,T1diag,conver=5,maxcycle=200)/6-31+G(d') Geom=AllCheck Guess=Read scf(maxcycle=1000)

06 June 2017 6,086 0 View

Why Transition state calculation is showing an error on CBS-QB3 level of theory ?

I have done some Transition state calculations on UB3LYP/cc-pVTZ level of theory and verified from IRC calculations too. Now i am trying same transition states calculations on CBS-QB3 level of...

06 June 2017 1,648 3 View

The method was applied by gaussian software for calculations of BSSE

I want to calculate the BSSE (basis set superposition error) for a ternary system. How do I calculate the BSSE using Gaussian counter poise for this system? Also, what method was applied by...

06 June 2017 818 3 View

A transition state which have imaginary frequency value 90 cm-1, IRC calculations are possible for this or not ?

During electronic structure calculations I am getting a transition state which have imaginary frequency value 90 cm-1 corresponding mode distance is 3.15 cm-1. When I am trying to do IRC...

06 June 2017 5,776 5 View

How to calculate the host-guest binding affinity using quantum mechanics

I'm trying to find out the binding affinity between the host-guest complex using Mopac. I have only the complexed and uncomplexed files. It would be helpful if someone could explain me with the...

06 June 2017 2,237 4 View

How to run a molecular orbital analysis for a particular atom?

I have optimized my geometry with B3LYP/6-31g(d). To plot the molecular orbital, I have done a single point calculation on the optimized geometries using the keyword pop=(nbo, full) gfinput. In...

06 June 2017 2,024 9 View

How to systematically study "HULA TWIST" in the cis-trans isomerization?

I want to study the mechanism of a cis-trans isomerization via HULA TWIST mechanism (computational study). Can anybody help in explaining the step by step procedure for the same? Is it possible to...

06 June 2017 732 6 View

Is it possibe to compute avoided crossings between triplet and singlet surfaces using CASSCF?

I conducted a scan in the ground state using M06-HF functional and cc-pVDZ basis set on the system which I am working. Then TDDFT single point energy calculations of the scanned structures were...

06 June 2017 1,431 5 View

Difference between zero-point corrected energies and Gibbs free energies

Hello everyone! I'm currently computing a quite big potential energy surface for a catalytic transformation. I'm using BP86/6-31G**/LANL2DZ for gas phase optimizations and M06L/6-311G**/SDDALL for...

06 June 2017 3,681 7 View

How can I know the structure was optimized or not?

Hello, I am very new user of Gaussian. I started the optimization of the connected two amino acids. Calculation was finished, and I would like to get the optimized structure. How can I know...

06 June 2017 7,179 5 View

What are the keywords for SMD descriptors (Molar volume, Thermal expansion coefficient, Absolute temperature, hydrogen bond basicity and so on )

I would like to know the keywords for the input of Gaussian 09 for the following descriptors of PCM-SMD model. Molar volume; Thermal expansion coefficient; absoulute temperature; numeral...

06 June 2017 4,025 10 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...

29 May 2017 9,546 8 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"...

23 May 2017 3,588 5 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.

21 May 2017 1,739 3 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...

20 May 2017 3,715 2 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...

18 May 2017 8,216 14 View

DFT computes, but B3LYP gives error

Hi I had the same error with a op+freq calculation in a big molecular system "140 atoms" at B3LYP/6-31G(dp) levels %mem=150MW # opt freq b3lyp/6-31g(d,p) geom=connectivity for optimization...

17 May 2017 6,867 4 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...

16 May 2017 572 6 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...

16 May 2017 6,057 3 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...

15 May 2017 6,903 14 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...

09 May 2017 961 4 View

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