CD-MUSIC
Charge Distribution Multi-Site Complexation — models metal adsorption on oxide mineral surfaces using a structurally-informed three-plane electrical double layer. References: Hiemstra & Van Riemsdijk, 1996; Bonten et al., 2008.
Model Parameters
Advanced: site densities, log KH, capacitances
Gibbsite has no verified CD-MUSIC set: supply both site densities and log KH. Hematite supplies site densities but requires log KH.
Metal Binding (optional)
Proton-only runs use Total Metal = 0 (literature-anchored). A metal run requires explicit log K_M and CD values; no verified Cu/Pb/Cd/Zn constants exist in this repository, so metal results are UNVERIFIED.
Mechanistic forward model: 1-pK MUSIC with an extended Stern layer (planes 0/1/2). It solves mass action, site balance, charge balance and the plane-potential equations — it does not clamp a logistic curve.
Supported Materials
- Iron oxides — Ferrihydrite, Goethite, Hematite
- Aluminum oxides — Gibbsite, Boehmite
- Manganese oxides — Birnessite
- Titanium dioxide — Rutile, Anatase
Theoretical Basis
- 1-pK MUSIC: each surface site has one protonation reaction (≡S−1/2 + H+ ⇌ ≡SH+1/2). Site densities are converted from sites nm−2 with the BET specific surface area.
- Extended Stern layer: three planes (0 = surface, 1 = inner Stern, 2 = outer Stern / diffuse-layer head). The Basic Stern model (BSM) is the special case C₂ → ∞, where planes 1 and 2 merge; it is used for the goethite parameter set.
- Solution: per pH point a damped Newton iteration solves mass action, site balance, the plane charge/potential equations and the Gouy–Chapman diffuse layer. Non-convergence is reported as an error — the result is never clamped or replaced by a logistic fallback.
- Metal binding: CD values distribute the metal charge over planes 0/1/2. No verified Cu/Pb/Cd/Zn log KM or CD values exist in this repository; a metal run is only performed with user-supplied values and its output is marked UNVERIFIED.
Key References
- Hiemstra & Zhao (2016) Environ. Sci.: Nano 3:1265–1279 — 1-pK MUSIC parameterization of ferrihydrite.
- Weng et al. (2006) J. Colloid Interface Sci. 302:442–457 — goethite CD-MUSIC / Basic Stern set.
- Hiemstra & Van Riemsdijk (1996) J. Colloid Interface Sci. 179:488–508 — surface structural charge distribution.
- Scope note: no external ferrihydrite/goethite metal-adsorption dataset is bundled. PZC, charge balance and limiting behaviour are consistency checks, not an independent predictive validation.