Questions tagged [computational-chemistry]

For questions about computational chemistry.

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17
votes
6answers
321 views

What are the applications of chemical graph theory?

Graph theory was originally introduced in computer science to study data structure. Chemists also introduced graph theory to study the relation between structure and properties for molecular compounds....
9
votes
1answer
387 views

High precision helium energy

In the paper "High Precision Theory of Atomic Helium", Drake lists the then best-known ground state energy of the Schrödinger equation for helium to 22 digits as: $$\lambda_0 \approx -2....
13
votes
2answers
271 views

How to get potential energy surface from GAMESS?

I'm trying to learn GAMESS and performing a simple PES scan of oxygen molecule. After the completion of the calculations I get a .log file with lots of sections like that: ...
24
votes
3answers
1k views

What does B3LYP do well? What does it do badly?

I have seen a general criticism of B3LYP in computational chemistry (especially with the 6-31G* basis set). I would like to know some of the more/less obvious problems that occur when using it and ...
13
votes
4answers
189 views

What is the role of a chemist in computational chemistry?

As someone that wants to learn about computational chemistry, mainly for its use in energy storage materials (and therefore DFT as the most practical method of it), I am wondering what is essential ...
7
votes
0answers
52 views

Excited states using ORMAS flag in GAMESS

I am trying to calculate the excited states using single reference CISD on $\ce{CH3OH},$ using ORMAS' CI-X option in GAMESS. As a test example I am using the $\ce{CH3OH}$ that has 2 core, 7 occ. ...
11
votes
2answers
240 views

One-center two-electron integrals between 1s STO

As per @user1271772 's suggestion I am asking this question here again. I am trying to understand SCF cycle by trying to code up solved example from Quantum Chemistry by Levine (page 443, 5th edition)...
10
votes
2answers
95 views

Analytic Hessians for meta-GGA functionals

In many of the free/open-source QM programs like GAMESS, ORCA, NWChem, the calculation of analytic hessians is not possible when a meta-GGA density functional is used, like M06-2X. My first question ...
8
votes
1answer
152 views

Which basis set should be used for a system that contains both anions and cations?

I am trying to model a system that has both anions and cations interacting with each other. (In this case it is calcium ion interacting with two small carboxylic acid molecules). Now, looking through ...