diff --git a/Framework/PythonInterface/mantid/api/src/FitFunctions/IFunctionAdapter.cpp b/Framework/PythonInterface/mantid/api/src/FitFunctions/IFunctionAdapter.cpp
index 94d69465072d..37457ea0db94 100644
--- a/Framework/PythonInterface/mantid/api/src/FitFunctions/IFunctionAdapter.cpp
+++ b/Framework/PythonInterface/mantid/api/src/FitFunctions/IFunctionAdapter.cpp
@@ -203,11 +203,12 @@ void IFunctionAdapter::setAttributePythonValue(IFunction &self, const std::strin
  * @param attr An attribute object
  */
 void IFunctionAdapter::setAttribute(const std::string &attName, const Attribute &attr) {
-  try {
+  auto self = getSelf();
+  if (typeHasAttribute(self, "setAttributeValue")) {
     object value = object(handle<>(getAttributeValue(*this, attr)));
-    callMethod<void, std::string, object>(getSelf(), "setAttributeValue", attName, value);
+    callMethod<void, std::string, object>(self, "setAttributeValue", attName, value);
     storeAttributeValue(attName, attr);
-  } catch (UndefinedAttributeError &) {
+  } else {
     IFunction::setAttribute(attName, attr);
   }
 }
diff --git a/Framework/PythonInterface/plugins/functions/TeixeiraWaterIqt.py b/Framework/PythonInterface/plugins/functions/TeixeiraWaterIqt.py
index 535a10a8dbf3..83ab6f0ae69b 100644
--- a/Framework/PythonInterface/plugins/functions/TeixeiraWaterIqt.py
+++ b/Framework/PythonInterface/plugins/functions/TeixeiraWaterIqt.py
@@ -5,16 +5,10 @@
 #     & Institut Laue - Langevin
 # SPDX - License - Identifier: GPL - 3.0 +
 # pylint: disable=no-init,invalid-name
-
-"""
-@author Spencer Howells, ISIS
-@date December 05, 2013
-"""
-
 import numpy as np
 
 from mantid.api import IFunction1D, FunctionFactory
-from scipy.special import spherical_jn  # bessel
+from scipy.special import spherical_jn
 
 
 class TeixeiraWaterIqt(IFunction1D):
@@ -32,46 +26,25 @@ def init(self):
         self.declareAttribute("Q", 0.4)
         self.declareAttribute("a", 0.98)
 
-    def setAttributeValue(self, name, value):
-        if name == "Q":
-            self.Q = value
-        if name == "a":
-            self.radius = value
-
     def function1D(self, xvals):
         amp = self.getParameterValue("Amp")
         tau1 = self.getParameterValue("Tau1")
         gamma = self.getParameterValue("Gamma")
+
+        q_value = self.getAttributeValue("Q")
+        radius = self.getAttributeValue("a")
+
         xvals = np.array(xvals)
 
-        qr = np.array(self.Q * self.radius)
+        qr = np.array(q_value * radius)
         j0 = spherical_jn(0, qr)
         j1 = spherical_jn(1, qr)
         j2 = spherical_jn(2, qr)
         with np.errstate(divide="ignore"):
-            rotational = j0 * j0 + 3 * j1 * j1 * np.exp(-xvals / (3 * tau1)) + 5 * j2 * j2 * np.exp(-xvals / tau1)
+            rotational = np.square(j0) + 3 * np.square(j1) * np.exp(-xvals / (3 * tau1)) + 5 * np.square(j2) * np.exp(-xvals / tau1)
             translational = np.exp(-gamma * xvals)
             iqt = amp * rotational * translational
         return iqt
 
-    def functionDeriv1D(self, xvals, jacobian):
-        amp = self.getParameterValue("Amp")
-        tau1 = self.getParameterValue("Tau1")
-        gamma = self.getParameterValue("Gamma")
-
-        qr = np.array(self.Q * self.radius)
-        j0 = spherical_jn(0, qr)
-        j1 = spherical_jn(1, qr)
-        j2 = spherical_jn(2, qr)
-        with np.errstate(divide="ignore"):
-            for i, x in enumerate(xvals, start=0):
-                rotational = j0 * j0 + 3 * j1 * j1 * np.exp(-x / (3 * tau1)) + 5 * j2 * j2 * np.exp(-x / tau1)
-                translational = np.exp(-gamma * x)
-                partial_tau = (x / np.square(tau1)) * (j1 * j1 * np.exp(-x / (3 * tau1)) + 5 * j2 * j2 * np.exp(-x / tau1))
-                jacobian.set(i, 0, rotational * translational)
-                jacobian.set(i, 1, amp * rotational * partial_tau)
-                jacobian.set(i, 2, -x * amp * rotational * translational)
-
 
-# Required to have Mantid recognise the new function
 FunctionFactory.subscribe(TeixeiraWaterIqt)
diff --git a/docs/source/release/v6.10.0/Inelastic/New_features/36502.rst b/docs/source/release/v6.10.0/Inelastic/New_features/36502.rst
index 307d11ce3025..ee7b8841219d 100644
--- a/docs/source/release/v6.10.0/Inelastic/New_features/36502.rst
+++ b/docs/source/release/v6.10.0/Inelastic/New_features/36502.rst
@@ -1 +1 @@
-- Added new `TeixeiraWaterIqt` fitting function, to fit linewidth and molecular residence time in intermediate scattering functions with Teixeira's model for water.
\ No newline at end of file
+- Added new `TeixeiraWaterIqt` fitting function, to fit linewidth and molecular residence time in intermediate scattering functions with Teixeira's model for water. This is now available in the IqtFit tab of the :ref:`QENS Fitting <interface-inelastic-qens-fitting>` interface.
diff --git a/qt/python/mantidqt/mantidqt/_common.sip b/qt/python/mantidqt/mantidqt/_common.sip
index 24583c80184b..57fb824407ff 100644
--- a/qt/python/mantidqt/mantidqt/_common.sip
+++ b/qt/python/mantidqt/mantidqt/_common.sip
@@ -351,7 +351,7 @@ public:
 
   UserSubWindow *createSubWindow(
       const QString &interface_name,
-      QWidget *parent = nullptr);
+      QWidget *parent = nullptr) throw(std::exception);
   QStringList getUserSubWindowKeys() const;
 
   void showHelpPage(const QString &url=QString());
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FitTabConstants.h b/qt/scientific_interfaces/Inelastic/QENSFitting/FitTabConstants.h
index 65869f518047..6eea73c572cb 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FitTabConstants.h
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FitTabConstants.h
@@ -23,6 +23,7 @@ static const auto FUNCTION_STRINGS =
                                                   {"Lorentzian", "L"},
                                                   {"StretchedExpFT", "SFT"},
                                                   {"TeixeiraWater", "TxWater"},
+                                                  {"TeixeiraWaterIqt", "TxWater"},
                                                   {"TeixeiraWaterSQE", "TxWater"},
                                                   {"FickDiffusionSQE", "FickDiff"},
                                                   {"ChudleyElliotSQE", "ChudElliot"},
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.cpp b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.cpp
index 116222dc0f72..ae3f44cb81c0 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.cpp
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.cpp
@@ -159,8 +159,6 @@ void ConvFunctionTemplateModel::checkSingleFunction(const IFunction_sptr &fun, b
   }
 }
 
-void ConvFunctionTemplateModel::setQValues(const std::vector<double> &qValues) { m_qValues = qValues; }
-
 void ConvFunctionTemplateModel::addFunction(std::string const &prefix, std::string const &funStr) {
   if (!prefix.empty())
     throw std::runtime_error("Function doesn't have member function with prefix " + prefix);
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.h b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.h
index 2fbf58840864..26bfd126845a 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.h
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ConvFunctionTemplateModel.h
@@ -41,7 +41,6 @@ class MANTIDQT_INELASTIC_DLL ConvFunctionTemplateModel : public MultiFunctionTem
   std::map<std::size_t, int> getSubTypes() const override;
   std::string setBackgroundA0(double value) override;
   void setResolution(const std::vector<std::pair<std::string, size_t>> &fitResolutions) override;
-  void setQValues(const std::vector<double> &qValues) override;
 
   bool hasDeltaFunction() const;
   bool hasTempCorrection() const;
@@ -55,7 +54,7 @@ class MANTIDQT_INELASTIC_DLL ConvFunctionTemplateModel : public MultiFunctionTem
   void applyParameterFunction(const std::function<void(ParamID)> &paramFun) const override;
 
   void clearData();
-  void setModel();
+  void setModel() override;
 
   std::optional<std::string> getLor1Prefix() const;
   std::optional<std::string> getLor2Prefix() const;
@@ -63,6 +62,7 @@ class MANTIDQT_INELASTIC_DLL ConvFunctionTemplateModel : public MultiFunctionTem
   std::optional<std::string> getDeltaPrefix() const;
   std::optional<std::string> getBackgroundPrefix() const;
 
+  std::string buildFunctionString(int const domainIndex) const override { return ""; }
   std::string buildLorentzianFunctionString() const;
   std::string buildTeixeiraFunctionString() const;
   std::string buildFickFunctionString() const;
@@ -96,7 +96,6 @@ class MANTIDQT_INELASTIC_DLL ConvFunctionTemplateModel : public MultiFunctionTem
   BackgroundSubType m_backgroundSubtype;
 
   std::vector<std::pair<std::string, size_t>> m_fitResolutions;
-  std::vector<double> m_qValues;
   bool m_isQDependentFunction = false;
 };
 
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.cpp b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.cpp
index 8d5116cf1037..8cf8e319c8f7 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.cpp
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.cpp
@@ -25,6 +25,8 @@ std::map<IqtTypes::FitType, TemplateSubTypeDescriptor> TemplateSubTypeImpl<IqtTy
     {IqtTypes::FitType::None, {"None", "", {ParamID::NONE, ParamID::NONE}}},
     {IqtTypes::FitType::StretchExponential,
      {"Stretch Exponential", "StretchExp", {ParamID::STRETCH_HEIGHT, ParamID::STRETCH_STRETCHING}}},
+    {IqtTypes::FitType::TeixeiraWaterIqt,
+     {"Teixeira Water Iqt", "TeixeiraWaterIqt", {ParamID::TWI_AMPLITUDE, ParamID::TWI_GAMMA}}},
 };
 
 template <>
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.h b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.h
index 60747ff8c64c..c7ad097ac663 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.h
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/FitTypes.h
@@ -23,7 +23,7 @@ enum class ExponentialType {
   TwoExponentials,
 };
 
-enum class FitType { None, StretchExponential };
+enum class FitType { None, StretchExponential, TeixeiraWaterIqt };
 
 enum class BackgroundType { None, Flat };
 
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.cpp b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.cpp
index b332b5d96c1e..7de3706b7477 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.cpp
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.cpp
@@ -64,11 +64,8 @@ void IqtFunctionTemplateModel::clearData() {
 }
 
 void IqtFunctionTemplateModel::setModel() {
-  m_model->setFunctionString(buildFunctionString());
-  m_model->setGlobalParameters(makeGlobalList());
-
+  MultiFunctionTemplateModel::setModel();
   tieIntensities();
-
   estimateFunctionParameters();
 }
 
@@ -82,6 +79,8 @@ void IqtFunctionTemplateModel::setFunction(IFunction_sptr fun) {
       m_exponentialType = ExponentialType::OneExponential;
     } else if (name == "StretchExp") {
       m_fitType = FitType::StretchExponential;
+    } else if (name == "TeixeiraWaterIqt") {
+      m_fitType = FitType::TeixeiraWaterIqt;
     } else if (name == "FlatBackground") {
       m_backgroundType = BackgroundType::Flat;
     } else {
@@ -91,7 +90,7 @@ void IqtFunctionTemplateModel::setFunction(IFunction_sptr fun) {
     return;
   }
   bool areExponentialsSet = false;
-  bool isStretchSet = false;
+  bool isFitTypeSet = false;
   bool isBackgroundSet = false;
   for (size_t i = 0; i < fun->nFunctions(); ++i) {
     auto f = fun->getFunction(i);
@@ -107,19 +106,23 @@ void IqtFunctionTemplateModel::setFunction(IFunction_sptr fun) {
         areExponentialsSet = true;
       }
     } else if (name == "StretchExp") {
-      if (isStretchSet) {
+      if (isFitTypeSet) {
         throw std::runtime_error("Function has wrong structure.");
       }
       m_fitType = FitType::StretchExponential;
       areExponentialsSet = true;
-      isStretchSet = true;
+      isFitTypeSet = true;
+    } else if (name == "TeixeiraWaterIqt") {
+      m_fitType = FitType::TeixeiraWaterIqt;
+      areExponentialsSet = true;
+      isFitTypeSet = true;
     } else if (name == "FlatBackground") {
       if (isBackgroundSet) {
         throw std::runtime_error("Function has wrong structure.");
       }
       m_backgroundType = BackgroundType::Flat;
       areExponentialsSet = true;
-      isStretchSet = true;
+      isFitTypeSet = true;
       isBackgroundSet = true;
     } else {
       clear();
@@ -146,10 +149,15 @@ void IqtFunctionTemplateModel::addFunction(std::string const &prefix, std::strin
       newPrefix = *getExp1Prefix();
     }
   } else if (name == "StretchExp") {
-    if (hasStretchExponential())
+    if (hasFitType(FitType::StretchExponential))
       throw std::runtime_error("Cannot add more stretched exponentials.");
     m_fitType = FitType::StretchExponential;
-    newPrefix = *getStretchPrefix();
+    newPrefix = *getFitTypePrefix(m_fitType);
+  } else if (name == "TeixeiraWaterIqt") {
+    if (hasFitType(FitType::TeixeiraWaterIqt))
+      throw std::runtime_error("Cannot add another TeixeiraWaterIqt function.");
+    m_fitType = FitType::TeixeiraWaterIqt;
+    newPrefix = *getFitTypePrefix(m_fitType);
   } else if (name == "FlatBackground") {
     if (hasBackground())
       throw std::runtime_error("Cannot add more backgrounds.");
@@ -213,7 +221,7 @@ void IqtFunctionTemplateModel::removeFunction(std::string const &prefix) {
     m_exponentialType = ExponentialType::OneExponential;
     return;
   }
-  prefix1 = getStretchPrefix();
+  prefix1 = getFitTypePrefix(m_fitType);
   if (prefix1 && *prefix1 == prefix) {
     m_fitType = FitType::None;
     return;
@@ -230,13 +238,14 @@ int IqtFunctionTemplateModel::numberOfExponentials() const { return static_cast<
 
 bool IqtFunctionTemplateModel::hasExponential() const { return m_exponentialType != ExponentialType::None; }
 
-bool IqtFunctionTemplateModel::hasStretchExponential() const { return m_fitType == FitType::StretchExponential; }
+bool IqtFunctionTemplateModel::hasFitType() const { return m_fitType != FitType::None; }
+
+bool IqtFunctionTemplateModel::hasFitType(FitType fitType) const { return m_fitType == fitType; }
 
 void IqtFunctionTemplateModel::removeBackground() {
   auto oldValues = getCurrentValues();
   m_backgroundType = BackgroundType::None;
-  m_model->setFunctionString(buildFunctionString());
-  m_model->setGlobalParameters(makeGlobalList());
+  setModel();
   setCurrentValues(oldValues);
 }
 
@@ -278,8 +287,6 @@ void IqtFunctionTemplateModel::setResolution(const std::vector<std::pair<std::st
   (void)fitResolutions;
 }
 
-void IqtFunctionTemplateModel::setQValues(const std::vector<double> &qValues) { (void)qValues; }
-
 void IqtFunctionTemplateModel::tieIntensities() {
   auto heightName = getParameterName(ParamID::STRETCH_HEIGHT);
   if (!heightName)
@@ -299,7 +306,9 @@ std::optional<std::string> IqtFunctionTemplateModel::getPrefix(ParamID name) con
   } else if (name <= ParamID::EXP2_LIFETIME) {
     return getExp2Prefix();
   } else if (name <= ParamID::STRETCH_STRETCHING) {
-    return getStretchPrefix();
+    return getFitTypePrefix(FitType::StretchExponential);
+  } else if (name <= ParamID::TWI_GAMMA) {
+    return getFitTypePrefix(FitType::TeixeiraWaterIqt);
   } else {
     return getBackgroundPrefix();
   }
@@ -314,11 +323,16 @@ void IqtFunctionTemplateModel::applyParameterFunction(const std::function<void(P
     paramFun(ParamID::EXP2_HEIGHT);
     paramFun(ParamID::EXP2_LIFETIME);
   }
-  if (hasStretchExponential()) {
+  if (hasFitType(FitType::StretchExponential)) {
     paramFun(ParamID::STRETCH_HEIGHT);
     paramFun(ParamID::STRETCH_LIFETIME);
     paramFun(ParamID::STRETCH_STRETCHING);
   }
+  if (hasFitType(FitType::TeixeiraWaterIqt)) {
+    paramFun(ParamID::TWI_AMPLITUDE);
+    paramFun(ParamID::TWI_TAU);
+    paramFun(ParamID::TWI_GAMMA);
+  }
   if (hasBackground()) {
     paramFun(ParamID::FLAT_BG_A0);
   }
@@ -333,11 +347,18 @@ std::string IqtFunctionTemplateModel::buildStretchExpFunctionString() const {
          "0,Lifetime>0,0<Stretching<1.001)";
 }
 
+std::string IqtFunctionTemplateModel::buildTeixeiraWaterIqtFunctionString(int const domainIndex) const {
+  auto const qValue = domainIndex < static_cast<int>(m_qValues.size()) ? m_qValues[domainIndex] : 0.4;
+  return "name=TeixeiraWaterIqt,Q=" + std::to_string(qValue) +
+         ",Amp=1,Tau1=0.05,Gamma=1.2,constraints=(Amp>"
+         "0,Tau1>0,Gamma>0)";
+}
+
 std::string IqtFunctionTemplateModel::buildBackgroundFunctionString() const {
   return "name=FlatBackground,A0=0,constraints=(A0>0)";
 }
 
-std::string IqtFunctionTemplateModel::buildFunctionString() const {
+std::string IqtFunctionTemplateModel::buildFunctionString(int const domainIndex) const {
   QStringList functions;
   if (hasExponential()) {
     functions << QString::fromStdString(buildExpDecayFunctionString());
@@ -345,9 +366,12 @@ std::string IqtFunctionTemplateModel::buildFunctionString() const {
   if (numberOfExponentials() > 1) {
     functions << QString::fromStdString(buildExpDecayFunctionString());
   }
-  if (hasStretchExponential()) {
+  if (hasFitType(FitType::StretchExponential)) {
     functions << QString::fromStdString(buildStretchExpFunctionString());
   }
+  if (hasFitType(FitType::TeixeiraWaterIqt)) {
+    functions << QString::fromStdString(buildTeixeiraWaterIqtFunctionString(domainIndex));
+  }
   if (hasBackground()) {
     functions << QString::fromStdString(buildBackgroundFunctionString());
   }
@@ -357,7 +381,7 @@ std::string IqtFunctionTemplateModel::buildFunctionString() const {
 std::optional<std::string> IqtFunctionTemplateModel::getExp1Prefix() const {
   if (!hasExponential())
     return std::optional<std::string>();
-  if (numberOfExponentials() == 1 && !hasStretchExponential() && !hasBackground())
+  if (numberOfExponentials() == 1 && !hasFitType() && !hasBackground())
     return std::string("");
   return std::string("f0.");
 }
@@ -368,8 +392,8 @@ std::optional<std::string> IqtFunctionTemplateModel::getExp2Prefix() const {
   return std::string("f1.");
 }
 
-std::optional<std::string> IqtFunctionTemplateModel::getStretchPrefix() const {
-  if (!hasStretchExponential())
+std::optional<std::string> IqtFunctionTemplateModel::getFitTypePrefix(FitType fitType) const {
+  if (!hasFitType(fitType))
     return std::optional<std::string>();
   if (!hasExponential() && !hasBackground())
     return std::string("");
@@ -379,9 +403,9 @@ std::optional<std::string> IqtFunctionTemplateModel::getStretchPrefix() const {
 std::optional<std::string> IqtFunctionTemplateModel::getBackgroundPrefix() const {
   if (!hasBackground())
     return std::optional<std::string>();
-  if (!hasExponential() && !hasStretchExponential())
+  if (!hasExponential() && !hasFitType())
     return std::string("");
-  return "f" + std::to_string(numberOfExponentials() + (hasStretchExponential() ? 1 : 0)) + ".";
+  return "f" + std::to_string(numberOfExponentials() + (hasFitType() ? 1 : 0)) + ".";
 }
 
 } // namespace MantidQt::CustomInterfaces::Inelastic
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.h b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.h
index b0990fd1c31f..9acb8a214522 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.h
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/IqtFunctionTemplateModel.h
@@ -36,11 +36,11 @@ class MANTIDQT_INELASTIC_DLL IqtFunctionTemplateModel : public MultiFunctionTemp
   std::map<std::size_t, int> getSubTypes() const override;
   std::string setBackgroundA0(double value) override;
   void setResolution(const std::vector<std::pair<std::string, size_t>> &fitResolutions) override;
-  void setQValues(const std::vector<double> &qValues) override;
 
   int numberOfExponentials() const;
   bool hasExponential() const;
-  bool hasStretchExponential() const;
+  bool hasFitType() const;
+  bool hasFitType(IqtTypes::FitType fitType) const;
   void removeBackground();
   bool hasBackground() const;
   void tieIntensities(bool on);
@@ -52,18 +52,19 @@ class MANTIDQT_INELASTIC_DLL IqtFunctionTemplateModel : public MultiFunctionTemp
   void applyParameterFunction(const std::function<void(ParamID)> &paramFun) const override;
 
   void clearData();
-  void setModel();
+  void setModel() override;
 
   void tieIntensities();
 
   std::optional<std::string> getExp1Prefix() const;
   std::optional<std::string> getExp2Prefix() const;
-  std::optional<std::string> getStretchPrefix() const;
+  std::optional<std::string> getFitTypePrefix(IqtTypes::FitType fitType) const;
   std::optional<std::string> getBackgroundPrefix() const;
 
-  std::string buildFunctionString() const;
+  std::string buildFunctionString(int const domainIndex) const override;
   std::string buildExpDecayFunctionString() const;
   std::string buildStretchExpFunctionString() const;
+  std::string buildTeixeiraWaterIqtFunctionString(int const domainIndex) const;
   std::string buildBackgroundFunctionString() const;
 
   IqtTypes::ExponentialType m_exponentialType = IqtTypes::ExponentialType::None;
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.cpp b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.cpp
index 5d985ccffaed..ea5eba5eb293 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.cpp
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.cpp
@@ -6,8 +6,10 @@
 // SPDX - License - Identifier: GPL - 3.0 +
 #include "MultiFunctionTemplateModel.h"
 
+#include "MantidAPI/FunctionFactory.h"
 #include "MantidAPI/IFunction.h"
 #include "MantidAPI/ITableWorkspace.h"
+#include "MantidAPI/MultiDomainFunction.h"
 
 namespace MantidQt::CustomInterfaces::Inelastic {
 
@@ -51,7 +53,10 @@ std::string MultiFunctionTemplateModel::getParameterDescription(std::string cons
 
 std::vector<std::string> MultiFunctionTemplateModel::getParameterNames() const { return m_model->getParameterNames(); }
 
-void MultiFunctionTemplateModel::setNumberDomains(int n) { m_model->setNumberDomains(n); }
+void MultiFunctionTemplateModel::setNumberDomains(int n) {
+  m_model->setNumberDomains(n);
+  setModel();
+}
 
 int MultiFunctionTemplateModel::getNumberDomains() const { return m_model->getNumberDomains(); }
 
@@ -175,6 +180,8 @@ void MultiFunctionTemplateModel::setGlobalParameterValue(std::string const &para
   m_model->setGlobalParameterValue(parameterName, value);
 }
 
+void MultiFunctionTemplateModel::setQValues(const std::vector<double> &qValues) { m_qValues = qValues; }
+
 void MultiFunctionTemplateModel::updateParameterEstimationData(DataForParameterEstimationCollection &&data) {
   m_estimationData = std::move(data);
 }
@@ -204,6 +211,24 @@ std::map<int, std::string> MultiFunctionTemplateModel::getParameterNameMap() con
   return out;
 }
 
+void MultiFunctionTemplateModel::setModel() {
+  auto multiDomainFunction = std::make_shared<MultiDomainFunction>();
+
+  for (int i = 0; i < m_model->getNumberDomains(); ++i) {
+    auto domainFunctionString = buildFunctionString(i);
+    if (domainFunctionString.empty()) {
+      break;
+    }
+    auto singleDomainFunction = FunctionFactory::Instance().createInitialized(domainFunctionString);
+    multiDomainFunction->addFunction(std::move(singleDomainFunction));
+    multiDomainFunction->setDomainIndex(i, i);
+  }
+
+  m_model->setFunction(std::move(multiDomainFunction));
+
+  m_model->setGlobalParameters(makeGlobalList());
+}
+
 std::vector<std::string> MultiFunctionTemplateModel::makeGlobalList() const {
   std::vector<std::string> globals;
   for (auto const id : m_globals) {
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.h b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.h
index 80f9f7e3de72..129b241a8b43 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.h
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/MultiFunctionTemplateModel.h
@@ -76,6 +76,8 @@ class MANTIDQT_INELASTIC_DLL MultiFunctionTemplateModel : public IFunctionModel
   virtual void setSubType(std::size_t subTypeIndex, int typeIndex) = 0;
   virtual std::map<std::size_t, int> getSubTypes() const = 0;
 
+  void setQValues(const std::vector<double> &qValues) override;
+
   virtual EstimationDataSelector getEstimationDataSelector() const = 0;
   void updateParameterEstimationData(DataForParameterEstimationCollection &&data);
   void estimateFunctionParameters();
@@ -85,6 +87,9 @@ class MANTIDQT_INELASTIC_DLL MultiFunctionTemplateModel : public IFunctionModel
   std::map<int, std::string> getParameterNameMap() const;
 
 protected:
+  virtual void setModel();
+  virtual std::string buildFunctionString(int const domainIndex) const = 0;
+
   void setParameter(ParamID name, double value);
   std::optional<std::string> getParameterName(ParamID name) const;
   void setCurrentValues(const std::map<ParamID, double> &);
@@ -93,6 +98,8 @@ class MANTIDQT_INELASTIC_DLL MultiFunctionTemplateModel : public IFunctionModel
   std::unique_ptr<FunctionModel> m_model;
   QList<ParamID> m_globals;
 
+  std::vector<double> m_qValues;
+
 private:
   double getParameter(ParamID name) const;
   double getParameterError(ParamID name) const;
diff --git a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ParamID.h b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ParamID.h
index bf2f1d87b90e..0bd9a2260e26 100644
--- a/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ParamID.h
+++ b/qt/scientific_interfaces/Inelastic/QENSFitting/FunctionBrowser/ParamID.h
@@ -23,6 +23,9 @@ enum class ParamID {
   STRETCH_HEIGHT,
   STRETCH_LIFETIME,
   STRETCH_STRETCHING,
+  TWI_AMPLITUDE,
+  TWI_TAU,
+  TWI_GAMMA,
   LOR1_AMPLITUDE,
   LOR1_PEAKCENTRE,
   LOR1_FWHM,
@@ -96,6 +99,9 @@ static std::map<ParamID, std::string> g_paramName{
     {ParamID::STRETCH_HEIGHT, "Height"},
     {ParamID::STRETCH_LIFETIME, "Lifetime"},
     {ParamID::STRETCH_STRETCHING, "Stretching"},
+    {ParamID::TWI_AMPLITUDE, "Amp"},
+    {ParamID::TWI_TAU, "Tau1"},
+    {ParamID::TWI_GAMMA, "Gamma"},
     {ParamID::LOR1_AMPLITUDE, "Amplitude"},
     {ParamID::LOR1_PEAKCENTRE, "PeakCentre"},
     {ParamID::LOR1_FWHM, "FWHM"},
diff --git a/qt/widgets/common/src/FunctionModel.cpp b/qt/widgets/common/src/FunctionModel.cpp
index f6e2fd703959..c2abdb4711d5 100644
--- a/qt/widgets/common/src/FunctionModel.cpp
+++ b/qt/widgets/common/src/FunctionModel.cpp
@@ -174,23 +174,23 @@ void FunctionModel::setParameterError(std::string const &parameterName, double v
 }
 
 double FunctionModel::getParameter(std::string const &parameterName) const {
-  return getCurrentFunction()->getParameter(parameterName);
+  auto const fun = getCurrentFunction();
+  return fun && fun->hasParameter(parameterName) ? fun->getParameter(parameterName) : 0.0;
 }
 
 IFunction::Attribute FunctionModel::getAttribute(std::string const &attrName) const {
-  return getCurrentFunction()->getAttribute(attrName);
+  auto const fun = getCurrentFunction();
+  return fun && fun->hasAttribute(attrName) ? fun->getAttribute(attrName) : IFunction::Attribute();
 }
 
 double FunctionModel::getParameterError(std::string const &parameterName) const {
   auto fun = getCurrentFunction();
-  auto const index = fun->parameterIndex(parameterName);
-  return fun->getError(index);
+  return fun && fun->hasParameter(parameterName) ? fun->getError(fun->parameterIndex(parameterName)) : 0.0;
 }
 
 std::string FunctionModel::getParameterDescription(std::string const &parameterName) const {
   auto fun = getCurrentFunction();
-  auto const index = fun->parameterIndex(parameterName);
-  return fun->parameterDescription(index);
+  return fun && fun->hasParameter(parameterName) ? fun->parameterDescription(fun->parameterIndex(parameterName)) : "";
 }
 
 bool FunctionModel::isParameterFixed(std::string const &parameterName) const {