Introduction to Quantum mechanics (semiemperical)

1. 1
Quantum Mechanics
Semiempirical Calculations
Abhijeet Kadam
TSEC
BioTechnology

2. 2
Semiempirical Calculations
● Quantum Mechanics + Expt. Values used
● Uses wave functions
– Slater type orbitals – STO
– Gaussian type orbitals – GTO
● Hydrogen like orbitals
● Treats linear combinations of orbitals by iterative
computations
– Establishes SELF-CONSISTANT field (SCF)
– And minimize energy of system

3. 3
Self-Consistant Feilds
● Differ in approximations
● Approximations which are made wrt repulsion
between electrons in different orbitals
● Approximations are adjusted by parameterizing
values to corrospond to
– Abinitio data
– Or expt. Available data

4. 4
History
● Earlier methods
– Huckel theory
– CNDO (Complete Neglect of Differential Overlap)
● The above methods
– Not reliable for geometry
– Not reliable for energy
– But good for calculating shapes of molecular orbits
and charges

5. 5
Improved Methods
● MINDO
– (Modified Intermediate Neglect of Differential Overlap)
● AMI
– (Atomic Modal Interpretation)
● MOPAC
– (Molecular Orbital PACkage)
● Above methods are parameterized be
– Lithium, berellium, boron, flourine, aluminium, Silicon,
Phosphorus, Sulphur, Chlorine, Zinc, Germanium, Bromium,
iodine, Tin, Mercury and Lead

6. 6
MOPAC
● Allows various
– Geometric Operations
– Geometric optimization
– With and without symmetry
– Vibrational energy calculations
– Atomic charge
– Dipole movement
– Ionization potential
– Bond order

7. 7
● Quantum Mechanics
● Semiempirical Calculations
● Self-Consistant Feilds
● History
● Improved Methods
● MOPAC