Dr. Gaurav Jhaa Blogs

  Density Functional Theory (DFT) is a computational quantum mechanical modeling method used in chemistry, physics, and materials science to investigate the electronic structure (the distribution of electrons) of molecules and solids. Here's a basic overview of how DFT calculations of molecules work:   1. **Formulation of the Problem**: In DFT, the problem is formulated as finding the electronic density that minimizes the total energy of the system. The electronic density is a function of position and represents the probability of finding an electron at a particular location.   2. **Approximations**: DFT involves several approximations, the most notable being the exchange-correlation functional. This functional captures the effects of electron-electron interactions, including exchange (the antisymmetry of the wave function) and correlation (the classical electrostatic repulsion between electrons).   3. **Choice of Basis Set**: In practical calculations, the electroni...

  Geometry optimization using Density Functional Theory (DFT) in Gaussian involves finding the minimum energy configuration of a molecule or molecular system by adjusting the nuclear coordinates iteratively until reaching convergence. Here's how you can perform geometry optimization using the DFT method in Gaussian:   1. **Input Preparation**:    Begin by preparing the input file for Gaussian. This file includes specifications for the molecule's geometry, the DFT method to be used, and any additional settings required for the calculation.   2. **Specify the DFT Method**:    Choose a DFT functional and basis set suitable for your system and the level of accuracy you require. Common DFT functionals include B3LYP, PBE, TPSS, etc. You'll also need to specify a basis set for describing the electronic structure, such as 6-31G(d), 6-311G(d,p), etc.   3. **Specify Optimization Keyword**:    Include the keyword "Opt" to indicate that a geometry o...

  HOMO and LUMO are terms used in chemistry to refer to the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), respectively. These orbitals are important in understanding the electronic structure and reactivity of molecules, especially in the context of organic and inorganic chemistry and chemical reactions.   HOMO (Highest Occupied Molecular Orbital):   The HOMO represents the highest energy level of molecular orbitals that contain electrons. It is typically involved in chemical bonding and determines the electron-donating properties of a molecule. In terms of significance: It dictates the reactivity of a molecule in nucleophilic reactions. Molecules with higher energy HOMOs are more prone to donate electrons and act as nucleophiles. It plays a crucial role in determining the absorption spectrum of molecules. Absorption of light often involves promotion of electrons from the HOMO to the LUMO or higher energy orbitals, depending ...

  IRC (Intrinsic Reaction Coordinate) calculations in Gaussian are used to explore the reaction pathways of chemical reactions. They allow you to follow the path of the reaction from reactants to products, revealing important intermediates and transition states along the reaction coordinate. Here's how you can perform IRC calculations in Gaussian: Performing the Reaction Coordinate Scan : Before running the IRC calculation, you typically perform a single-point energy calculation or a geometry optimization at each point along the reaction coordinate. This involves scanning the reaction coordinate by varying the geometry of the system along the desired direction. Specify the IRC Keyword : To request an IRC calculation in Gaussian, you need to include the "IRC" keyword in your input file. This tells Gaussian to perform the IRC calculation starting from a specified transition state or reaction intermediate. Transition ...

Phonon dispersion calculations are a crucial aspect of computational materials science and condensed matter physics. They play a significant role in understanding the vibrational properties of crystalline materials, which are essential for predicting various physical properties and phenomena. Here's an introduction to the significance of phonon dispersion calculations:   Understanding Lattice Dynamics: Phonon dispersion calculations provide insights into the lattice dynamics of crystalline materials. Phonons are quantized lattice vibrations, and their dispersion relation (relationship between phonon frequency and wave vector) characterizes the vibrational behavior of the crystal lattice.   Thermal Properties: Phonon dispersion calculations are fundamental for understanding thermal properties such as heat capacity, thermal conductivity, and lattice thermal expansion. These properties are crucial for engineering materials for specific applications, such as thermoelectric materia...

 In Gaussian, NBO (Natural Bond Orbital) calculations are used to analyze the bonding patterns within molecules based on their electronic structure. NBO analysis provides insights into the nature of chemical bonding, including the characterization of bond types, lone pairs, and delocalization effects. Here's how you can perform an NBO calculation in Gaussian: Specify the NBO Keyword: To request NBO analysis in Gaussian, you need to include the "NBO" keyword in your input file. This instructs Gaussian to perform the NBO calculation as part of the electronic structure calculation. Perform an Electronic Structure Calculation: Before running the NBO analysis, you typically perform an electronic structure calculation (e.g., Hartree-Fock, DFT, MP2, etc.) to obtain the molecular orbitals and electron density. The type of calculation you choose depends on your specific research question or the level of theory appropriate for your system. Input Example: Here's an example of ho...

 Non-covalent interactions are important in understanding the behavior of molecules and materials in chemistry and biology. These interactions include hydrogen bonds, van der Waals forces, electrostatic interactions, and more. Calculating and analyzing non-covalent interactions can be crucial for predicting molecular structures, binding affinities, and other properties. Here's a general guide on how to calculate and analyze non-covalent interactions: 1. Software and Tools: You'll need specialized software or tools to perform quantum mechanical calculations or molecular dynamics simulations. Some popular options include Gaussian, DFT (Density Functional Theory) programs, and molecular modeling software like VMD, PyMOL, and Gaussian. 2. Geometry Optimization: Start by optimizing the geometry of the molecules or complexes of interest. This involves finding the lowest energy structure by minimizing the potential energy surface. 3. Identify Non-Covalent Interactions: Once you have o...

#CASTEP #dmol3 #nanomaterials #dft #dftcalculations #quantumchemistry #dftvideos #dfttutorials #materialsstudio #PES #Gaussian #Gaussview #spartan #forcite #quantumguruji #gauravjhaa #homolumo #dftstudy A set of standard basis sets is stored internally in Gaussian; these basis sets may be specified by including the appropriate keyword within the route section for the calculation. The Gen keyword allows a user-specified basis set to be used in a Gaussian calculation. It is used in place of a basis set keyword or a density-fitting basis set keyword. In this case, the basis set description must be provided as input (in a separate basis set input section). Gen may be analogously used to specify an alternate density fitting basis set (see the examples). The GenECP variation may be used to read in both basis functions and ECPs; it is equivalent to Gen Pseudo=Read. It is designed for use in ONIOM calculations in which you want to use a general basis set with ECPs within one ONIOM layer.

  Gaussian Common Errors and Solutions Link Error Message L1 ntrex1 Illegal ITpye or MSType generated by parse QPErr L101 End of file in Zsymb Found a string as input There are no atoms in this input structure Symbol not found in Z-matrix Variable index is out of range (Case 1) Variable index is out of range (Case 2) Attempt to redefine unrecognized symbol L103 Error imposing constraints FormBX had a problem Maximum of*** iterations exceeded in RedStp Linear search skipped for unknown reason Inconsistency: ModMin= N Eigenvalue= MM L108 Variable has invalid number of steps L114 Error in INITNF L123 Delta-x Convergence NOT Met GS2 Optimization Failure L202 Problem with the distance matrix Atom too close Change in point group or standard orientation FO...