For some flexibility...

src/d2_base.cpp

 #include <tadah/models/descriptors/d2/d2_base.h>
 
 std::vector<std::string> D2_Base::get_init_atoms(Config &c) {
+  if (!c.exist("TYPE2B")) {
+    std::cerr << "Warning: TYPE2B key was not found. "
+      "Atom pairs must be initialized manually." << std::endl;
+    return {};
+  }
   std::vector<std::string> init_atoms(c.size("TYPE2B"));
   c.get("TYPE2B", init_atoms);
   init_atoms.erase(init_atoms.begin(), init_atoms.begin() + nparams+1);

src/d_base.cpp

@@ -115,10 +115,32 @@ void D_Base::init_for_atoms(const std::vector<std::string> &Zs) {
   if (Zs.size() % 2 != 0) {
     throw std::invalid_argument("The vector size must be even.");
   }
-  for (size_t i=0; i< Zs.size(); i+=2) {
-    int Zi = PeriodicTable::find_by_symbol(Zs[i]).Z;
-    int Zj = PeriodicTable::find_by_symbol(Zs[i+1]).Z;
-    init_for_atoms(Zi, Zj);
+  
+  for (size_t i = 0; i < Zs.size(); i += 2) {
+    if (Zs[i] == "*" && is_number(Zs[i+1])) {
+      int Zj = PeriodicTable::find_by_symbol(Zs[i+1]).Z;
+      for (int Zi = 1; Zi < 119; ++Zi) {
+        init_for_atoms(Zi, Zj);
+      }
+    } 
+    else if (Zs[i+1] == "*" && is_number(Zs[i])) {
+      int Zi = PeriodicTable::find_by_symbol(Zs[i]).Z;
+      for (int Zj = 1; Zj < 119; ++Zj) {
+        init_for_atoms(Zi, Zj);
+      }
+    } 
+    else if (Zs[i] == "*" && Zs[i+1] == "*") {
+      for (int Zi = 1; Zi < 119; ++Zi) {
+        for (int Zj = Zi; Zj < 119; ++Zj) {
+          init_for_atoms(Zi, Zj);
+        }
+      }
+    } 
+    else {
+      int Zi = PeriodicTable::find_by_symbol(Zs[i]).Z;
+      int Zj = PeriodicTable::find_by_symbol(Zs[i+1]).Z;
+      init_for_atoms(Zi, Zj);
+    }
   }
 }
 std::vector<std::string> D_Base::get_init_atoms(Config &c, std::string type) {

src/dm_base.cpp

@@ -3,8 +3,13 @@ void DM_Base::set_rfidx(size_t rfidx_) { rfidx=rfidx_; }
 size_t DM_Base::get_rfidx() { return rfidx; }
 
 std::vector<std::string> DM_Base::get_init_atoms(Config &c) {
+  if (!c.exist("TYPEMB")) {
+    std::cerr << "Warning: TYPEMB key was not found. "
+      "Atom pairs must be initialized manually." << std::endl;
+    return {};
+  }
   std::vector<std::string> init_atoms(c.size("TYPEMB"));
   c.get("TYPEMB", init_atoms);
-  init_atoms.erase(init_atoms.begin(), init_atoms.begin() + nparams+1);
+  init_atoms.erase(init_atoms.begin(), init_atoms.begin() + nparams + 1);
   return init_atoms;
 }