#psi4
Every note tagged #psi4, newest first — or browse the full archive.
One donor, one acceptor, one new band: push–pull chromophores and charge transfer
Aniline and nitrobenzene each absorb only in the ultraviolet. Bolt the amino donor and the nitro acceptor onto the same ring and a new band appears that neither parent owns — lower in energy and brighter than anything either shows alone. This post computes that emergence with TD-DFT, measures the charge-transfer character directly, and uses it to stress-test two density functionals against a failure mode one of them is famous for.
How much does correlation really cost? The correlation gap in water, measured
The Hartree–Fock post drew its correlation-gap figure schematically. This post runs the actual calculations — RHF marched up a basis-set ladder to its limit, MP2 and CCSD(T) below it — and reports what electron correlation costs, in hartrees, for one bent molecule of water.
Two barriers, one tunnel: the hydrogen peroxide torsion, recomputed
The original version of this post validated its H2O2 torsional barrier against the wrong experimental number and reported tunneling corrections from code that assumed its own conclusions. Recomputed from scratch — a fresh MP2/cc-pVTZ relaxed scan, the periodic torsional Schrödinger equation solved on the resulting potential, and transmission through the barrier that actually matters — with the tunneling splitting checked against sixty years of far-infrared spectroscopy.
Three exact solutions and one inequality: quantum chemistry's ground floor, computed
The particle in a box, the harmonic oscillator, and the hydrogen atom are the only systems in quantum chemistry you can solve with pen and paper — which makes them the only place you can hold your numerics fully accountable. Every figure here is computed, every number is checked against its closed form, and a psi4 basis ladder shows the one atom where Hartree–Fock is the whole answer.
Setting Up a Comprehensive Quantum Chemistry Environment on Linux
A detailed guide for establishing a versatile computational chemistry environment on Linux systems with instructions for package installation, environment configuration, and remote access setup.
Polarizability Trends in Carbon-Chalcogen Diatomic Molecules - A Computational Study
A systematic computational investigation of polarizability in diatomic molecules formed between carbon and Group 16 (O, S, Se, Te) elements, with analysis of geometry-optimized structures and higher-order electronic properties.
Polarizability Trends in Group 14-16 Heteronuclear Molecules - A Computational Study
A systematic computational investigation of polarizability trends in diatomic molecules formed between Group 14 (C, Si, Ge, Sn, Pb) and Group 16 (O, S, Se, Te) elements, showcasing the power of automation and open-source computational chemistry tools.
Quantum Chemical Calculations of Hyperpolarizability - Setup and Initial Results
A detailed walkthrough of setting up computational environment for calculating hyperpolarizabilities of Group 4A elements
Calculating Atomic Polarizabilities of Group 14 Elements Using Psi4 - A Finite Field Approach
An experimental study calculating polarizabilities of Group 14 elements using Psi4's finite field method, with results for C, Si, and Ge, and insights into limitations for heavier elements.