Quantumchemistry

with

Gaussian98W

Starting the program - Click on:

“Arbeitsplatz”->”export on earth”->”G98w”->g98w.exe”

Input for a job: The Z-Matrix

To create a new Gaussian Input click on:

File->New

A new “Job Entry” window appears.

Meaning of different sections:

% Section: Optional, used for machine specific commands like maximum memory usage etc.

Route Section: Gaussian Keywords go here. We use:

HF STO-3G OPT

Title Section: A title for your job (MUST have one!)

Charge & Multiplicity: molecular charge (-1, 0, 1 ..) and Multiplicity (2S+1): 1 for singlet.

Molecule Specification:

(Starting) Geometry of the molecule to be calculated. Either in Cartesian Coordinates or by defining the connection of the atoms within the molecule (internal coordinates, the so called

“Z-Matrix”)

The Z-Matrix

One line for each atom.

O Symbol of first atom

H 1 r1 Second Atom + distance to one other atom (here: to Atom 1)

H 1 r1 2 w1 Third Atom + distance to one other atom plus angle to two other atoms (angle: 3 -1-2)

r1 0.9 Starting value for variable r1

w1 105. Starting value for

variable w1

Z-Matrix for NH₃

X

N 1 1.0

H 2 r1 1 w1

H 2 r1 1 w1 3 120. <- dihedral angle

H 3 r1 1 w1 3 240.

r1 1.0

w1 120.

The dihedral angle:

Formal definition: angle between the planes

2-1-3 and 2-1-4