Ensembles and SOC-NAMD¶
.oqp control reference
Use canonical routes and controls in input files. Raw names
identify implementation storage. A control without an accepted canonical
spelling is not available in .oqp files.
Nuclear Ensemble¶
ensemble¶
Use the physical route or primary calculation for this control; see the canonical spelling and ownership. Do not write this raw storage key as a separate input section.
| Value | Current support |
|---|---|
nve |
Default; no thermostat after the initial velocity is prepared. |
nvt |
Langevin thermostat at temperature with damping friction. |
npt |
Reserved but currently rejected. |
NPT requires a QM/MM energy evaluation for every barostat trial box. The
current ESPF-QM/MM driver does not provide that trial-box energy, so OpenQP
rejects ensemble=npt rather than performing an invalid NPT simulation.
friction is in ps⁻¹ and defaults to 1.0; it must be positive for NVT. The
legacy thermostat keyword accepts off or langevin and maps to
ensemble=nve or ensemble=nvt. In legacy md input, the corresponding
scalar names are init_temp, thermostat_temperature, and
thermostat_friction (default 1.0 ps⁻¹).
The NVE energy criteria are documented separately under NAMD Diagnostics. They do not apply to thermostat energy exchange in NVT.
Adaptive Nuclear Timestep¶
| Keyword | Default | Meaning |
|---|---|---|
dt_adaptive |
False |
Reduce the timestep when the displacement criterion requires it. |
dt_min |
0.05 fs |
Smallest allowed adaptive timestep. |
dx_max |
0.02 bohr |
Largest accepted per-step atomic displacement. |
Adaptive stepping is a separate integration option. Case-D energy-triggered substepping repeats one nominal interval from the same phase point and is documented under NAMD Numerical Continuity.
SOC-NAMD¶
Development status
SOC-NAMD, including SOC-NAMD-QMMM, is still under active development and must be treated as experimental. The inputs and restart records are available for method development and numerical verification, but their availability does not establish that the present force and coupling approximations are ready for production scientific conclusions. Report the selected basis and all approximations with any result.
A complete input with a reference trajectory is in the formaldehyde SOC-NAMD worked example.
soc¶
Use the physical route or primary calculation for this control; see the canonical spelling and ownership. Do not write this raw storage key as a separate input section.
Default: False. soc=True enables surface hopping with spin--orbit coupling
among ns singlets and nt triplets. Each triplet contributes three
(M_S) sublevels, giving ns + 3*nt MCH basis functions before
spin-adiabatic transformation.
soc_basis¶
Use the physical route or primary calculation for this control; see the canonical spelling and ownership. Do not write this raw storage key as a separate input section.
| Value | Meaning |
|---|---|
adiabatic |
Propagate spin-adiabatic SOC eigenstates; the force uses the weighted-MCH approximation. |
mch |
Propagate the spin-pure MCH basis with the active-root MCH gradient. |
Default: adiabatic. For current development and numerical verification, the
mch form is preferred because it avoids the approximate weighted force of
the spin-adiabatic implementation. This preference does not change the
experimental status of SOC-NAMD.
init_state¶
Use the physical route or primary calculation for this control; see the canonical spelling and ownership. Do not write this raw storage key as a separate input section.
Optional zero-based MCH character label such as S0, S1, T0, or T1.
It selects the initial spin-adiabatic state with the largest matching MCH
character and overrides active in an SOC calculation.
Spin-adiabatic force diagnostics¶
| Keyword | Default | Meaning |
|---|---|---|
grad_wthr |
0.001 |
Minimum MCH weight included in the weighted diagonal gradient. |
soc_du_dt_corr |
False |
Add a finite-difference eigenvector-change correction. |
soc_tdc_grad_corr |
False |
Add an approximate TDC-projected gradient correction. |
econs |
False |
Rescale every step as a temporary energy-drift stabilizer. |
These controls examine the approximate spin-adiabatic force and are not needed
for soc_basis=mch. econs is not a substitute for a physically consistent
force and should remain off unless a documented diagnostic requires it.
QM/MM SOC-NAMD¶
Adding qmmm(...) selects the corresponding SOC-QM/MM driver. See
SOC-NAMD-QMMM for the dispatch table and the
current force and coupling approximations.