Input Preparation
Introduction
To do a computational chemistry simulation, you have to give a program with the data of molecule or method that you want to study and use, respectively, that it have to be sufficiently initial information for computing afterward. We call the code that can help us to calculate that program, a file that include the information of molecular structure that input, and a file that include the results that output.
Most program packages in computational chemistry basically have the same idea and concept. Description of preparation of input file to calculation of electronics structure properties of molecule are used in format of Gaussian program which is invented by John A. Pople, one of the Father of computational chemistry in 20st century. The Gaussian program is the role model of many code in present. Since it has high performance and providing high accuracy results in range of comparable with experimental results, the whole scientist around the world choose Gaussian as a main program to do their research.
Structure of Input File
The syntax or structure of Gaussian input is friendly interface with user even with who is novice in computational chemistry, and also can be written flexibly and easily adaptable. There is only one way to create an input file as following below
Syntax of input file: sample_of_input_file.inp
%chk=your_input_name.chk%mem=M%nprocshare=N# Job task, method of calculation, and optional keyword are here----- black line -----Comment is here, you can write anything on this line.----- black line -----Charge of molecule, multiplicity number of moleculeThe first line of Cartesian coordinate (XYZ) of molecule........The last line of of Cartesian coordinate (XYZ) of molecule** Noted that the text in bold is important.
The assignment of resource requirement is also important.
You have to define two thing about machine performance.
1. How much total memory you want to use ? = M
Example. %mem=800MW
%mem=5000MB
%mem=2GB
2.How many CPUs you want to use ? = N
Example. %nprocs=1
%nprocs=4
**Note that the memory unit can be KB, MB, GB, TB, KW, MW, GW or TW.
Example of Gaussian Input File
File: test001.inp
%chk=test001.chk%mem=1GB%nprocs=4# TEST OPT STO-3G OPTCYC=2 scf=conventionalGaussian Test Job 10, STO-3G FLETCHER-POWELL OPTIMIZATION OF WATER0 1O 0.000 0.000 0.000H 1.000 0.000 0.000H 0.000 1.000 0.000File: test002.inp
%chk=test002.chk%mem=500MW%nprocs=1#P TEST STO-3G COMPLEX pop=full scf=tightGaussian Test Job 01, SINGLET DELTA STO-3G//STO-3G DIOXYGEN0 1O O 1 RR 1.220*** You should leave a few blank line at the end of input file.