## What is self consistent field theory?

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The self-consistent field method is an iterative method that involves selecting an approximate Hamiltonian, solving the Schrödinger equation to obtain a more accurate set of orbitals, and then solving the Schrödinger equation again with theses until the results converge.

### Is Casscf size consistent?

Even though multi-reference methods like CASSCF and NOCI are size consistent, and perturbation theory methods like MP2 are size consistent; the combination of the two are not guaranteed to be size consistent.

#### What is SCF in chemistry?

A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid.

**Is full CI variational?**

Full configuration interaction (or full CI) is a linear variational approach which provides numerically exact solutions (within the infinitely flexible complete basis set) to the electronic time-independent, non-relativistic Schrödinger equation.

**What is correlation energy?**

The correlation energy is defined as the difference between the total energy E0 and that in the Hartree-Fock approximation. From: Strongly Coupled Plasma Physics, 1990.

## What is self consistency?

n. 1. behavior or traits that have a high degree of internal harmony and stability.

### What is the Hartree-Fock method?

The Hartree-Fock (HF) method is a variational method that provides the wave function of a many-body system assumed to be in the form of a Slater determinant for fermions and of a product wave function for bosons.

#### What is Psi4?

Psi4 is an open-source suite of ab initio quantum chemistry programs designed for efficient, high-accuracy simulations of molecular properties. We routinely perform computations with >2500 basis functions on multi-core machines.

**What is Fermi correlation?**

This prevents two parallel-spin electrons being found at the same point in space. This kind of correlation is often referred to as Fermi correlation. The major deficiency is the neglect of the correlation between the spatial position of electrons with opposite spin due to their Coulomb repulsion.