2.2 H₂ binding curve: cancellation with consistent references

These are unexecuted teaching inputs and starting models. Original diagrams are schematics, not calculated results. Validate version-specific syntax, licensed or authorized data, numerical convergence and the scientific model before using this workflow.

2.2.1 Model, units and provenance

PW cutoffs and energies use Ry, common force output uses Ry/bohr, and pressure uses kbar. Geometry cards state their coordinate units. Different executables have distinct grammars and time-unit conventions.

Shared inputs, conventions and evidence

Original schematic: H₂ binding curve: cancellation with consistent references. No numerical results are claimed.

2.2.2 Unexecuted inputs and explicit deltas

Use the accompanying instructions to identify the parent calculation and placement of every delta; a snippet is not automatically a standalone input. Preserve all blank-line and file-provenance requirements.

2.2.2.1 Input block 1

! CONTROL: new prefix='h2_r074', outdir='./scratch/h2_r074'
! SYSTEM: nat=2; remove nspin and tot_magnetization
! Keep ibrav=1, A=16.0 and converged cutoffs
ATOMIC_POSITIONS angstrom
H 8.0 8.0 7.63
H 8.0 8.0 8.37
K_POINTS gamma

2.2.3 Worked investigation

2.2.3.1 Intuition and prerequisites

A molecular binding curve is an energy difference between well-defined states, not the raw total energy of the molecule. Reuse the H pseudopotential and numerical settings from 2.1, and build neutral H₂ with a singlet-like non-spin-polarized treatment near equilibrium. Stretching a restricted single-determinant description far toward dissociation introduces a separate electronic-structure limitation; convergence alone cannot repair it.

2.2.3.2 Original delta to the H input

See input block 1 above.

2.2.3.3 Outputs, checks and exercise

Produce a table of distance, converged SCF energy, atomic reference, ΔE and maximum force. Compare the numerical derivative of E(r) with the force component along the bond, respecting that moving both atoms changes r. Tighten the electronic threshold until this comparison is stable. Repeat a near-minimum and a stretched point in a larger box. Exercise: distinguish electronic binding energy, zero-point-corrected dissociation energy and finite-temperature free energy; state what additional calculation each requires.