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

How to get the accessible surface area from Gaussian or Spartan?

It seems that the Gaussian output provides the Cavity area only. Is it possible for using Gaussian to get accessible surface area for organic compounds? Do I need to add any keyword in the input...

03 March 2017 3,370 3 View

CISD on CIS excited states?

Hi, i was wondering if it is possible to calculate CISD energies on CIS excited states through the checkpoint file in gaussian09...could we simply read the checkpoint file, use guess=read and...

03 March 2017 434 4 View

Guassian QST3 output has 1 imaginary frequency but I don't think it is the correct TS. What should I do?

I ran a QST3 calculation under an expanded basis set: S 0 6-311+G(2df,p) **** H C N O 0 6-311+G(d,p) **** (this is the same expanded basis set I used for optimizations) When the calculation...

03 March 2017 2,766 3 View

How to calculate adsorption energy?

Hi there, How to calculate adsorption energy for computational catalytic study if the bare catalyst, complex, and reactant are stable in different spin multiplicities? e.g., bare catalyst slab's...

03 March 2017 7,140 9 View

How to use couple cluster model for excited state optimization?

I am willing to optimize dimer in both, singlet and triplet, excited state. But I don't know whether it is possible from gaussian, and if yes, how to do. Thanks in advance.

03 March 2017 2,709 4 View

How to decide periodicity and phase shift angle from torsinal scan graph obtained via QM calculation ? (Force Field Parameter Development for CHARMM)

I am trying to parameterize a small organic molecule namely L(+)Lactate and I am having problems with the dihedral fitting procedure. I have 360 degree of torsional scan for each dihedral angle in...

03 March 2017 6,959 2 View

Why my frequency calculation aborted?

Hello, I am trying to running a frequency calculation with gaussian for a dimer that is made by benzene and bromine fluoride at T-shape. After finding a stationary point in the optimization, the...

03 March 2017 5,425 2 View

Any success increasing basis sets between TS searches in Gaussian?

Hi all, I'm not actually asking for help, I'm more interested in opinions. I will usually perform all OPT reactant and product at a basis set of 3-21G (because they are very quick and my molecule...

03 March 2017 2,642 11 View

Missing lone pair non bonding electrons in water MO diagram?

MO diagram obtained by Gaussian calculations based on HF wave function with 6-31G** basis set indicate only one pair of non bonding electrons. However based on VB theory Oxygen atom of water...

03 March 2017 2,741 5 View

Is there any scientific support for using part of an optimized structure in freq. calculation?

I optimized a two-layer ONIOM structure. Is there any scientific support for using part of the optimized structure in freq. calculation?

03 March 2017 1,626 0 View

In VEDA Software Which Vibrations Are "Asymmetric" or "Symmetric"?

Hi, I calculated PED datas with VEDA but I don't know which vibrations are asymmetric or symetric. How could I decide it? For example: s 1 1.00 STRE 13 18 CH 1.086848 f3207...

03 March 2017 8,045 4 View

In VEDA Software Which Vibrations Are "Asymmetric" or "Symmetric"?

Hi, I calculated PED data with VEDA but I don't know which vibrations are asymmetric or symetric. How could I decide it? For example: s 1 1.00 STRE 13 18 CH 1.086848 f3207...

02 March 2017 7,995 3 View

How does one do a loop in Gaussian?

Hello, thank you for your help. So first of all I have a lot of .gjf files (Gaussian acceptable format) and I want to run Gaussian on all of them to get energy log files. I think that's a...

18 February 2017 9,101 5 View

Is it possible to open an incomplete Gaussian checkpoint file in GView?

If you perform a restart on any Gaussian job it will write over the contents of the earlier .log/.out file. Typically, an incomplete log./.out file can be loaded in GView showing the results thus...

17 February 2017 4,197 3 View

How to run natural energy decomposition analysis in Gamess with b3lyp/6-311++g(d,p) basis sets?

I carry out the natural energy decomposition analysis (NEDA) on gamess with b3lyp/6-311++g(d,p) level for the complex in the less distances of the local minimum but unfortunately, the output is...

15 February 2017 7,331 2 View

TS calculation in Gaussian leads to too many imaginary frequencies?

I am trying to find a transition state for a nucleophile addition and my jobs never seem to converge. Calculating the force constants at the final geometry shows multiple negative frequencies, the...

13 February 2017 8,327 4 View

How to avoid convergence failure in composite ab initio methods ( a set of predefined calculations)?

I am using Gaussian09 to run a structure minimisation on a molecular system that is radical cationic using the composite method ROCBS-4M. The input structure has already been optimised at...

07 February 2017 8,489 3 View

What are effects of solvent polarity on the electronic spectrum??

i) I would need to know the relation between the dipole moment of the solute and the polarity of the solvent. ii) How the dipole moment of the solute decrease in n → π* transition but increase...

06 February 2017 9,778 3 View

How can i adjust the value of long range parameter µ by using IOP (3/107) and IOP (3/108)?

How can i adjust the value of long range parameter µ for long range calculations like WB97XD in Gaussian09 A02???? I try to use IOP (3/107) and IOP (3/108) but I get an error using...

05 February 2017 2,704 3 View

In Gaussian, do we apply counterpoise correction during geometry optimization or in a single point calculation on the optimized system?

I'm performing an interaction energy calculation between two molecules. I want to apply CP correction for BSSE. My question is, during geometry optimization of the complex, do I have to apply the...

04 February 2017 1,190 14 View

How to avoid convergence failure in composite ab initio methods ( a set of predefined calculations)?

I am using Gaussian09 to run a structure minimisation on a molecular system that is radical cationic using the composite method ROCBS-4M. The input structure has already been optimised at...

02 February 2017 6,508 4 View

How can i adjust the value of long range parameter µ by using IOP (3/107) and IOP (3/108)?

How can i adjust the value of long range parameter µ for long range calculations like WB97XD in Gaussian09 A02???? I try to use IOP (3/107) and IOP (3/108) but I get an error using...

02 February 2017 405 4 View

What are effects of solvent polarity on the electronic spectrum??

i) I would need to know the relation between the dipole moment of the solute and the polarity of the solvent. ii) How the dipole moment of the solute decrease in n → π* transition but increase...

02 February 2017 9,849 4 View

In Gaussian, do we apply counterpoise correction during geometry optimization or in a single point calculation on the optimized system?

I'm performing an interaction energy calculation between two molecules. I want to apply CP correction for BSSE. My question is, during geometry optimization of the complex, do I have to apply the...

02 February 2017 10,062 15 View

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