diff --git a/Cargo.toml b/Cargo.toml
index aedef87ae..1981fb17e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -42,7 +42,6 @@ libm = "0.2"
 gauss-quad = "0.2"
 approx = "0.5"
 criterion = "0.5"
-arrayvec = "0.7"
 
 feos-core = { version = "0.8", path = "crates/feos-core" }
 feos-dft = { version = "0.8", path = "crates/feos-dft" }
diff --git a/crates/feos-core/Cargo.toml b/crates/feos-core/Cargo.toml
index 14b0d19a7..7d88fa5c8 100644
--- a/crates/feos-core/Cargo.toml
+++ b/crates/feos-core/Cargo.toml
@@ -27,7 +27,6 @@ indexmap = { workspace = true, features = ["serde"] }
 rayon = { workspace = true, optional = true }
 typenum = { workspace = true }
 itertools = { workspace = true }
-arrayvec = { workspace = true, features = ["serde"] }
 
 [dev-dependencies]
 approx = { workspace = true }
diff --git a/crates/feos-core/src/parameter/association.rs b/crates/feos-core/src/parameter/association.rs
index b87f57df9..dcdbcfc88 100644
--- a/crates/feos-core/src/parameter/association.rs
+++ b/crates/feos-core/src/parameter/association.rs
@@ -1,19 +1,16 @@
 use super::{BinaryParameters, BinaryRecord, GroupCount, PureParameters};
 use crate::{FeosError, FeosResult, parameter::PureRecord};
-use arrayvec::ArrayString;
 use ndarray::Array1;
 use num_traits::Zero;
 use serde::{Deserialize, Serialize};
 use std::collections::{HashMap, HashSet};
 
-type SiteId = ArrayString<8>;
-
 /// Pure component association parameters.
-#[derive(Serialize, Deserialize, Clone, Copy, Debug)]
+#[derive(Serialize, Deserialize, Clone, Debug)]
 pub struct AssociationRecord<A> {
-    #[serde(skip_serializing_if = "SiteId::is_empty")]
+    #[serde(skip_serializing_if = "String::is_empty")]
     #[serde(default)]
-    pub id: SiteId,
+    pub id: String,
     #[serde(flatten)]
     pub parameters: Option<A>,
     /// \# of association sites of type A
@@ -35,7 +32,7 @@ impl<A> AssociationRecord<A> {
         Self::with_id(Default::default(), parameters, na, nb, nc)
     }
 
-    pub fn with_id(id: SiteId, parameters: Option<A>, na: f64, nb: f64, nc: f64) -> Self {
+    pub fn with_id(id: String, parameters: Option<A>, na: f64, nb: f64, nc: f64) -> Self {
         Self {
             id,
             parameters,
@@ -47,16 +44,16 @@ impl<A> AssociationRecord<A> {
 }
 
 /// Binary association parameters.
-#[derive(Serialize, Deserialize, Clone, Copy, Debug)]
+#[derive(Serialize, Deserialize, Clone, Debug)]
 pub struct BinaryAssociationRecord<A> {
     // Identifier of the association site on the first molecule.
-    #[serde(skip_serializing_if = "SiteId::is_empty")]
+    #[serde(skip_serializing_if = "String::is_empty")]
     #[serde(default)]
-    pub id1: SiteId,
+    pub id1: String,
     // Identifier of the association site on the second molecule.
-    #[serde(skip_serializing_if = "SiteId::is_empty")]
+    #[serde(skip_serializing_if = "String::is_empty")]
     #[serde(default)]
-    pub id2: SiteId,
+    pub id2: String,
     // Binary association parameters
     #[serde(flatten)]
     pub parameters: A,
@@ -67,7 +64,7 @@ impl<A> BinaryAssociationRecord<A> {
         Self::with_id(Default::default(), Default::default(), parameters)
     }
 
-    pub fn with_id(id1: SiteId, id2: SiteId, parameters: A) -> Self {
+    pub fn with_id(id1: String, id2: String, parameters: A) -> Self {
         Self {
             id1,
             id2,
@@ -76,16 +73,16 @@ impl<A> BinaryAssociationRecord<A> {
     }
 }
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Debug)]
 pub struct AssociationSite<A> {
     pub assoc_comp: usize,
-    pub id: SiteId,
+    pub id: String,
     pub n: f64,
     pub parameters: A,
 }
 
 impl<A> AssociationSite<A> {
-    fn new(assoc_comp: usize, id: SiteId, n: f64, parameters: A) -> Self {
+    fn new(assoc_comp: usize, id: String, n: f64, parameters: A) -> Self {
         Self {
             assoc_comp,
             id,
@@ -120,13 +117,28 @@ impl<A: Clone> AssociationParameters<A> {
             for site in record.association_sites.iter() {
                 let par = &site.parameters;
                 if site.na > 0.0 {
-                    sites_a.push(AssociationSite::new(i, site.id, site.na, par.clone()));
+                    sites_a.push(AssociationSite::new(
+                        i,
+                        site.id.clone(),
+                        site.na,
+                        par.clone(),
+                    ));
                 }
                 if site.nb > 0.0 {
-                    sites_b.push(AssociationSite::new(i, site.id, site.nb, par.clone()));
+                    sites_b.push(AssociationSite::new(
+                        i,
+                        site.id.clone(),
+                        site.nb,
+                        par.clone(),
+                    ));
                 }
                 if site.nc > 0.0 {
-                    sites_c.push(AssociationSite::new(i, site.id, site.nc, par.clone()));
+                    sites_c.push(AssociationSite::new(
+                        i,
+                        site.id.clone(),
+                        site.nc,
+                        par.clone(),
+                    ));
                 }
             }
         }
@@ -212,15 +224,15 @@ impl<A: Clone> AssociationParameters<A> {
                 let par = &site.parameters;
                 if site.na > 0.0 {
                     let na = site.na * record.count.into_f64();
-                    sites_a.push(AssociationSite::new(i, site.id, na, par.clone()));
+                    sites_a.push(AssociationSite::new(i, site.id.clone(), na, par.clone()));
                 }
                 if site.nb > 0.0 {
                     let nb = site.nb * record.count.into_f64();
-                    sites_b.push(AssociationSite::new(i, site.id, nb, par.clone()));
+                    sites_b.push(AssociationSite::new(i, site.id.clone(), nb, par.clone()));
                 }
                 if site.nc > 0.0 {
                     let nc = site.nc * record.count.into_f64();
-                    sites_c.push(AssociationSite::new(i, site.id, nc, par.clone()));
+                    sites_c.push(AssociationSite::new(i, site.id.clone(), nc, par.clone()));
                 }
             }
         }
diff --git a/crates/feos-core/src/parameter/mod.rs b/crates/feos-core/src/parameter/mod.rs
index 5b40bc0ef..6cc8904ac 100644
--- a/crates/feos-core/src/parameter/mod.rs
+++ b/crates/feos-core/src/parameter/mod.rs
@@ -252,6 +252,15 @@ impl<P: Clone, B: Clone, A: Clone> Parameters<P, B, A> {
             .iter()
             .enumerate()
             .array_combinations()
+            .chain(
+                // Somehow there is no array_combinations_with_replacement in itertools
+                // ii combinations are not intuitive here, but potentially needed for
+                // molecules with multiple association sites.
+                pure_records
+                    .iter()
+                    .enumerate()
+                    .map(|(i, p)| [(i, p), (i, p)]),
+            )
             .map(|[(i1, p1), (i2, p2)]| {
                 let Some(id1) = p1.identifier.as_str(identifier_option) else {
                     return Err(FeosError::MissingParameters(format!(
diff --git a/crates/feos/Cargo.toml b/crates/feos/Cargo.toml
index 319e98fb1..137532aea 100644
--- a/crates/feos/Cargo.toml
+++ b/crates/feos/Cargo.toml
@@ -22,7 +22,6 @@ indexmap = { workspace = true }
 rayon = { workspace = true, optional = true }
 itertools = { workspace = true }
 typenum = { workspace = true }
-arrayvec = { workspace = true, features = ["serde"] }
 
 feos-core = { workspace = true }
 feos-derive = { workspace = true }