Dear  Nguyen,

Below are the NIST site that gives the solution of many computational chemistry examples. You can choose any example and compare your results with the results presented in the site to check your answers. This site also lists methods and basis functions of different complexity.

http://cccbdb.nist.gov/

Dear Nguyen Duong Nguyen,

There are two types of calculation methods: (1) Quantum Mechanics (QM) methods which include ab initio such as HF, MP2, MP3 and etc., DFT (B3LYP 6-31G (d,p), B3LYP 6-311G with or depolarized  or diffused functions and etc. and semi-empirical such as AM1, PM3 and etc. (2) Molecular Mechanics methods such as MM2, MM3 and etc.

Generally ab initio methods can handle molecules with size up to 30 atoms. HF and STO-3G are lowest bases within ab initio since they contain many approximations, however, they relatively fast and do not consume a lengthy computer time. 

MP2, MP3 & MP4 with the different basis sets are more accurate ab initio methods however, they are computer time consuming.

On the other hand, DFT with a variety of basis sets can handle molecules with size up to 70 atoms and their calculation results are fairly good and agree with experimental values. 

Please note that you can use a variety of bases sets when calculating using ab inito or DFT methods. For a list of available basis sets, please use the following link:

http://www.gaussian.com/g_tech/g_ur/m_basis_sets.htm

Semi-empirical methods such as PM3, AM1, MNDO, MINDO/3 and etc can handle molecules with a size larger than 100 atoms. These methods are good for initial optimization and  for calculating heats of formation.

Quantum mechanics aims to solve the schroedinger equation for a set of electrons that must move around on a certain framework of nuclei. thus what you are finding is the electronic structure of a molecule. quantum mechanical methods can be used to predict molecular structure, because you can propose a wide spectrum of structures, calculate their electronic structures and relative energies.

Molecular Mechanics (Vibrational Spectroscopy) assumes that molecules are held together by a relatively small set of forces that are modeled by simple mathematical equations : The motions of the nuclei are studied and the electrons are not explicitly examined at all, but are assumed to find an optimal distribution about the nuclei.Molecular mechanics is presently the only practical method for calculations on very large molecules or for conformational searching on highly flexible molecules. MMFF94, in particular, has proven to be a reliable and fast tool for conformational analysis. There are no atom limits for molecular mechanics calculations.  the molecular mechanics model does not involve electrons explicitly and does not involve any solution of the schroedinger equation, although there are a number of "hybrid" techniques that combine molecular mechanics with very simple quantum models to deal with things like resonance (QM/MM).

Attached please find a file which contains A Guide to Molecular Mechanics and

Quantum Chemical Calculations.

Hoping this will be helpful,

Rafik

Dear Mr. Mudar,

Thanks for your recommend. However, it's just mention about "simple" chemical reagent. About my model, it's okay with medium computation; but I cannot apply it for huge computation. What's a pity!

Dear Mr. Rapik,

Thanks for your ebook, but it's not exact book I want. Actually, it's not so deep, but it's still quite deep. At the moment, I used 2 tutorial: first is Gaussian 09W tutorial of Anna Tomberg, second is tutorial about DFT of Orca employment (https://www.youtube.com/watch?v=U6NBxzH8G2A). Two reasons I love them is (1) they said that "alway first thing to do ....", it's so great. When I have good experience, I can change my first thing; but now, when I don't know much, the tutorial such as "first thing, next thing..." is the best. Next, (2) is they said about the error maybe happen, and how to solve it. Especially, the support of Orca is so great, easy to understand, no fee, and variable (I feel sad about Gaussian too much).

Anyway, thanks for your answer :)

Mr./Miss/Mrs. Nguyen,

In order to conduct a relevance computation using the mentioned in your positing program packages, it is better to recognize with the content of refs. 1 and 2. There are shown almost all available methods of quantum chemistry with a useful summary about advantages, limits and applicability to each of them. This knowledge allows to obtain a meaningful information about different properties of given molecular object. There are shown examples of computations and data encompassing from low molecular weight substances to (bio)macromolecules of organics, inorganic, metal-organics and organometallic; in addition to 0D-3D material with multi-functional application.

The publications are not literature source for educational purposes, because of these are length restricted sources focusing the attention of the readers on the scientific novelty as results/data/theories. They aim to recognize the audience with new scientific achievements/findings. The authors have taken into consideration that the potential readers have basic knowledge towards different computational methods. The goal and the character of a "publication" as scientific literature source are completely different from those of textbooks, monographs, lecture notes and so on.

Towards parallel running of Gaussian, there is able to do this. You should use different supporting programs, in parallel to an independent computation via Gaussian's window itself. If you operate with 2 versions of Gaussian, you can run 4-5 parallel computations (even more if you have available more then one supporting programs).

1. Computational Molecular Science, P. Schreiner, W. Allen, M. Orozco, P. Willett (Eds.), Vols 1 - 6 (pp. 1 - 3041), Wiley, Chichester, 2014.

2. Encyclopedia of Computational Chemistry, PvR Schleyer, N. Allinger, J. Gasteiger, P. Kollman, H. Schaefer III, P. Schreiner (Eds.), Vols. 1 - 5 (pp. 1 - 3375), Wiley, Chichester, 1998.