Writing canonical keywords

Write a route, one primary calculation, optional controls, then geometry. The route chooses the electronic-structure model; the primary calculation chooses the physical quantity. A section call supplies advanced settings. Translate the physical calculation into canonical syntax; changing a filename does not translate its contents.

mrsf(nstate=3)/bhhlyp/6-31g* grad(S1) scf(conv=1e-8)
geom="water.xyz"

Here mrsf(nstate=3)/bhhlyp/6-31g* is the route, grad(S1) is the primary calculation and scf(conv=1e-8) is an advanced call. Geometry paths are relative to the input file, not the shell working directory. Use a quoted path or a triple-quoted coordinate block. No leading # route marker or section headers are used.

Routes, physical states and defaults

Request	Internal configuration	Interpretation
hf/sto-3g	input.method=hf, scf.type=rhf	Singlet HF; omitted driver is energy.
dft/pbe0/def2-svp	input.method=hf, input.functional=pbe0	DFT uses the HF/KS SCF driver internally.
mrsf(nstate=3)/bhhlyp/6-31g*	input.method=tdhf, tdhf.type=mrsf, tdhf.nstate=3	Three singlet response states if no other target is selected.
mrsf/... grad(S1)	properties.grad=2, tdhf.multiplicity=1	Second singlet response root; the physical first excited singlet.
mrsf/... opt(T0)	optimize.istate=1, tdhf.multiplicity=3	Lowest triplet target; the ROHF reference is selected automatically.
sf/... grad(root=1)	properties.grad=1	Spin character must be examined after diagonalization.
tddft/... grad(S0)	input.method=hf, state 0	Ground-state HF/DFT derivative, unlike MRSF S0.

The abbreviated ... rows explain mappings and are not runnable files. Downloadable complete examples are on Migration and verification.

For MRSF, S0, T0, and Q0 each mean the lowest state of the chosen spin multiplicity. They are not energy-ordered across multiplicities. Do not specify the automatic high-spin reference with mult or scf(multiplicity=...). For ordinary HF/DFT, mult selects the reference multiplicity. Explicit rohf/roks require mult>=2.

A default has three distinct meanings:

1. The parser supplies an omitted driver or physical state.
2. The schema supplies omitted section values and converts their types.
3. The calculation may apply an effective default or performance preset.

The generated tables list raw schema defaults, not a promise of the final effective value. Follow each detailed reference for units, ranges, effective defaults, and restrictions. nstate without an explicit value is inferred from requested roots (at least one); namd defaults to physical S1. The namd lowering supplies scf.conv, tdhf.conv, and tdhf.zvconv=1e-8 only where an explicit value has not already been set.

Main calculations and advanced controls

Purpose	Canonical form	Detailed reference
Energy / derivative	energy, grad(S0)	Electronic structure
SCF and quadrature	scf(conv=1e-8), dftgrid(pruned=none)	SCF
Response solver	route nstate; tdhf(nvdav=30)	Excited states
Optimization	opt(S0,maxit=100,coordsys=tric)	Geometry
Crossing points	meci(S0,S1), mecp(S0,T0)	Geometry
Frequencies	hess(S0,type=analytical)	Geometry
Nonadiabatic coupling	nac(S0,S1,type=analytical)	Response
Nuclear dynamics	md(nstep=10,dt=0.5)	Dynamics
Surface hopping	namd(S1,scheme=Overlap) md(nstep=10,dt=0.5)	Dynamics
QM/MM	add qmmm(...) to a supported driver	QM/MM
Environment / execution	pcm(...), omp_threads=8	Environment

Signatures here locate the controls; they do not establish that every model, property, derivative, or combination is supported. The full driver signatures and the calculation validator apply. namd(...) md(...) is the specific permitted composition: it is one excited-state dynamics calculation, not two independent drivers. Other combinations such as grad(S1) opt(S1) are rejected.

Conflicts, aliases and ownership

The source inventory classifies every schema key:

Ownership	How to write it
Generic	A keyword-only section(key=value) call; the same section/key is passed onward.
Route/driver	Use route, globals, or primary-driver controls. Do not copy internal section keys mechanically.
Legacy only	No canonical input spelling; compatible Python API only.
Intentionally forbidden	No canonical equivalent; retained internally for compatibility.
Unmapped	A documentation audit gap, not evidence of support.

Aliases normalize to one public spelling. threads means omp_threads; geometry and system mean geom. Giving both aliases is an error, not a last-value-wins rule. Flat basis or functional must agree with the route. Reserved method/state/reference selectors cannot override it. Old oqp(...) calls are read-time compatibility forms folded into the geometry driver; new input puts those options in opt(...), ts(...), or another applicable driver.

Legacy optimizer, step_size, step_tol, mep_maxit, the geometric section and legacy NEB k/maxg/avgg/optep controls are not canonical options. Native NEB spring/fmax/frms/opt_ends differ in semantics or units. Convert them deliberately.