The document discusses computational chemistry methods for calculating various thermodynamic and electronic properties of molecules. It provides an overview of computational chemistry and the properties that can be calculated, such as structure, energy, dipole moment, polarizability, ionization potential, HOMO/LUMO energies, chemical hardness and softness. It also describes different computational methods like classical molecular mechanics and molecular dynamics, as well as quantum chemistry methods including semi-empirical, ab initio and density functional theory approaches. Specific examples are given of calculating properties like dipole moment, polarizability, ionization potential using computational methods.

1. Calculating the thermodynamic
properties, HOMO, LUMO,
Ionization potentials,
chemical hardness and softness,
dipole moment, polarizability.
T.MANIKANTHA
2 M.Sc, chemistry
REG NO: 18107
SRI SATHYA SAI INSTITUTE OF HIGHER LEARNING (deemed university)
PCHM - 305

2. Introduction:
• Computational chemistry uses result of theoretical chemistry
incorporated into efficient computer programmed to calculate
structure and properties of molecule.
• It calculate the properties of molecule such as structure,
relative energy, charge distribution, dipole moment, vibrational
frequency, polarizability, reactivity and other spectroscopic
quantity.
• Computational chemistry range from highly accurate (Ab initio
method to less accurate (semi emiprical) to very approximate
(molecular mechanics).
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3. Advantage of Computational
Chemistry:
1) It allows the medicinal chemist for use the computational power of
computer for measurement of
Mol. geometry
electron density
electrostatic potentional
conformational analysis
different types of energies.
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4. 2) Determination of structure of ligand and target through X-ray
crystallography and NMR spectroscopy.
3) Docking of ligand in rececpter active sites and exact measerment of
geometric and energetic favor ability of such interaction.
4) Comparssion of various ligands throgth various parameters.
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5. What does Computational
Chemistry Calculate ?
• Energy, Structure and Properties
• What is the energy for a given geometry?
• How does energy vary when geometry changes?
• Which geometries are stable?
• How do atoms rearranges to form new molecules?
• How do stucture, energy, and properties change over time?
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6. Examples
• Ionization energy (HOMO energy).
• Electron affinity (LUMO energy).
• Proton affinity.
• Electronic excitation energy (UV-Vis spectra).
• NMR chemical shifts and coupling constants.
• Reaction path and barrier height.
• Reaction rate.
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7. Computational method
There are two main types method depending on the starting point theory.
• • Classical method :- Are those method use Newton mechanics to model
molecular system.
• • Quantum chemistry method:-Which makes use of Quantum mechanics to
model the molecular system. This method used different type of
approximation to solve Schrödinger’s Equation.
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8. Classical Methods
1. Molecular Mechanics
2. Molecular Dynamics.
Quantum Mechanics Methods
1. Semi empirical Methods.
2. Ab initio Methods.
3. Density functional Theory.
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9. Quantum Mechanics Method
1. Ab inito method
2. Semiemperical method
3. Density functional theory
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10. Ab Initio method
• Ab initio translated from Latin means from “first principles”
• This refers to the fact that no experimental data is used and computations
are based on quantum mechanics.
• It derived directly from theoretical principle
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11. Different Levels of Ab Initio Calculations
• 1. Hartree-Fock (HF)
• 2. Density Functional Theory (DFT)
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12. Hartree-Fock (HF)
• • The simplest ab initio calculation.
• • It based on Central field approximation.
• • The major disadvantage of HF calculations is that electron correlation is
not taken into consideration.
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13. Density Functional Theory
• • Considered an ab initio method, but different from other ab initio
methods because the wave function is not used to describe a molecule
• • Density functional theory in which total energy is expressed in term of
total electron density is used.
• • DFT methods take less computational time than HF calculations and are
considered more accurate.
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14. Ab initio calculations of elastic constants and
thermodynamic properties
of NiAl under high pressures
Hongzhi Fu a,*, Dehua Li b, Feng Peng a, Tao Gao c,
Xinlu Cheng c
Thermodynamic properties
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15. • NiAl possesses the stable B2(cP2) crystal structure, which consists of two
interpenetrating primitive cubic cells, where Al atoms occupy the cube
corners of one sub lattice and Ni atoms occupy the cube corners of the
second sub lattice. NiAl has been studied extensively as a potential
structure material in the aerospace industry for over three decades because
of its high melting temperature, low density, good environmental
resistance, high thermal conductivity, attractive modulus, etc.
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17. Computational methods:
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19. Dipole moment
• A dipole moment is a measurement of the separation of two opposite
electrical charges. Dipole moments are a vector quantity. The magnitude is
equal to the charge multiplied by the distance between the charges and the
direction is from negative charge to positive charge: μ = q · r.
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20. • The permanent moments of a molecule are important descriptors of the ground state charge
distribution. The ability of a certain theoretical model to reproduce experimental permanent
dipole moments is therefore very helpful in assessing the quality of the corresponding
electron probability distribution.
• There have been numerous investigations of dipole moments at the Hartree-Fock and post-
HF levels which underline the importance of electron correlation for reaching accurate
results. The most famous example in this respect is probably the carbon monoxide
molecule, whose experimental dipole moment amounts to 0.11 D with the negative end at
the carbon atom, i. e., being of –C=O+ polarity. The Hartree-Fock approximation is not
even able to reproduce this qualitative orientation. Near the HF limit (i. e., using a very
large, almost complete one-electron basis set) a dipole moment of –0.28 D is calculated, i.
e., the HF dipole moment has the reverse orientation, +C=O–.
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21. • Modern approximate density functional theory performs much better.
• μ = μx + μ + μ along the molecular axis from several recent investigations
involving typical approximate exchange-correlation functionals (the
negative sign in case of CO indicates a +C=O– polarity).
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22. • All functionals employed, including the simple local density
approximation provide dipole moments for carbon monoxide which not
only show the correct –C=O+ orientation, but also give very satisfactory
quantitative results. For the totally uncorrelated HF and the partially
correlated MP2 wave function methods, Cohen and Tantirungrotechai,
1999, report mean absolute deviations of 0.17 and 0.05 D for the dipole
moments of the ten small molecules of their test set.
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23. • Because the electric dipole moment is an expectation value of a one-
electron operator, it is expected to be predicted relatively well by a
Hartree-Fock wave function or high quality SCF functions.
• The purpose of this note is to compare observed molecular dipole moments
with a set of theoretical values which were produced in SCF calculations
on molecules with a uniform basis set of Gaussians
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24. • The wave functions employed for the 34 linear and nonlinear molecules of
this study were SCF single determinants constructed from a basis set2 of
two contracted functions per atomic orbital, each contraction being a linear
combination of Gaussian primitive functions.
• The basis contains only sand p Gaussians on second row atoms and s on
hydrogen. Thus it contains no polarization functions; d or higher spherical
harmonics on second row atoms, and p or higher on hydrogen
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26. Polarizability
• Polarizability allows us to better understand the interactions between
nonpolar atoms and molecules and other electrically charged species, such
as ions or polar molecules with dipole moments
• Atomic and molecular polarizabilities are important properties in many
areas. For example a large fraction of the electrostatic intermolecular
interaction energy is related to this quantity, in particular for systems
without a permanent dipole moment.
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27. • can be computed by numerical differentiation of the field-dependent
energy or dipole moment.
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29. HOMO , LUMO
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36. Ionization potential
•The ionization energy or ionization potential is
the energy necessary to remove an electron from
the neutral atom. It is a minimum for the alkali
metals which have a single electron outside a
closed shell. It generally increases across a row
on the periodic maximum for the noble gases
which have closed shells.
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39. • All computational procedure was carried out using Gaussian 09 and
Gaussian view 5.08 programs. The optimization structure of Cycloheptane,
7-monosilicon-Cycloheptane and 7-monosilicon–7-hydroxyl-Cycloheptane
molecules with substitution Silicon and hydroxyl in positions of Hydrogen
atom have been performed with B3LYP/CC-PVDZ level in the gas phase
and DFT method. The energy of the highest occupied molecular orbital is
EHOMO and the energy of the lowest unoccupied molecular orbital is
ELUMO. The energy gap computed using the following equation
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41. • The values of electronic properties such as IP, EA and X are computed by
DFT/B3LYP with CC-PVDZ. The ionization potential have been computed
by making 7-monosilicon-Cycloheptane one electron deficit. These
quantities give us an idea about the chemical reactivity of substitute
Cycloheptane
• the electron distribution of Silicon is 3s2 3p2 and Oxygen 2p4 are assumed
to be inactive in chemical bonding with the Carbon atoms. For this, the
electron substitution leads to decreasing the values of ionization potential
(IP) and electronegativity (X), while the values of electron affinity (EA)
are increasing.
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43. Chemical hardness and softness:
• The determination of the specific sites at which the interaction between
two chemical species is going to occur, is of fundamental importance to
determine the path and the products of a given reaction.
• In principle, from a theoretical viewpoint, one should calculate the
potential energy surface associated with the interacting species, to obtain
the reaction coordinate that allows one to establish the path followed by the
reacting molecules to reach the transition state and the final products.
• Chemical reactivity, in order to show that the hardness and softness
concepts provide fundamental information about the changes in energy
associated with the interaction of chemical species.
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44. 1. The density functional theory framework
Density functional theory provides an alternative approach to the description of the
electronic structure of atoms and molecules, in principle more simple than
conventional wave function theory, because the total energy is determined directly
from the electronic density distribution p(r), through the expression
• where F[p] is the universal Hohen berg-Kohn functional, and v(r) is the external
potential generated by the nuclei. The functional F[p] is given by the sum of the
kinetic T[p], the classical Coulomb interaction J[p], and the exchange-correlation
Exc[P ] energy density functionals,
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47. References:
1.Basis set effects on relative energies and HOMO–LUMO energy gaps of fullerene C36
2.Structure and electronic properties of substitutionally doped Cycloheptane molecule using DFT, raja k.
mohammad et al.
https://doi.org/10.1016/j.rinp.2016.11.039
3.Computational Study of Geometry, Solvation Free Energy, Dipole Moment, Polarizability, Hyperpolarizability
and Molecular Properties of 2-Methylimidazole
Mohammad firoz khan et al.
4. Chemical hardness and density functional theory
RALPH G PEARSON
Chemistry Department, University of California, Santa Barbara, CA 93106, USA
5. A HARDNESS AND SOFTNESS THEORY OF BOND ENERGIES AND CHEMICAL REACTIVITY, Jos6 L.
G~zquez
Kyoung Hoon Kim Young-Kyu Han jaehoon Jung
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48. Thank you
SAIRAM…….,