Add Builtin LDA Electron-Proton Correlation Functionals (#38)

* first commit

* grabbed lda epcs from libxc

* add epc functional options

* enable more epc interface

* added is_epc check and start generating tests

* attemp to add tests for epc lda functionals

* Remove unwanted changes

* skip ground truth comparison for epc functionals and allow is_epc trait to automatically generate

* Update generate_primitive_kernels.py

* change epc checking logic in tests

* check if spin is polarized before constructing epc kernel

* pre libxc7 epc=false

bin/generate_primitive_kernels.py

@@ -472,7 +472,7 @@ def get_const_lines( self, _xc_lines, xc_vars ):
 
 class GenMetaData:
   def __init__( self, local_name, libxc_file, ofname, xc_type, dens_tol, exx_coeff,
-    params = {}, needs_laplacian = False, is_kedf = False ):
+    params = {}, needs_laplacian = False, is_kedf = False, is_epc = False ):
     self.local_name = local_name
     self.libxc_file = libxc_file
     self.ofname     = ofname
@@ -482,6 +482,7 @@ def __init__( self, local_name, libxc_file, ofname, xc_type, dens_tol, exx_coeff
     self.params     = params
     self.needs_laplacian = needs_laplacian
     self.is_kedf = is_kedf
+    self.is_epc  = is_epc
 
     self.is_hyb = abs(float(exx_coeff)) > 1e-10
 
@@ -493,6 +494,46 @@ def __init__( self, local_name, libxc_file, ofname, xc_type, dens_tol, exx_coeff
 kernel_prefix = 'include/exchcxx/impl/builtin/kernels/'
 gen_table = {
 
+  'EPC17_1' : GenMetaData( 'BuiltinEPC17_1', 
+    libxc_prefix + 'lda_exc/lda_c_epc17.c', 
+    kernel_prefix + 'epc17_1.hpp',
+    'LDA', 1e-24, 0.,
+    { 'a': '2.35',
+      'b': '2.40',
+      'c': '3.20' },
+    False, False, True 
+    ),
+
+  'EPC17_2' : GenMetaData( 'BuiltinEPC17_2', 
+    libxc_prefix + 'lda_exc/lda_c_epc17.c', 
+    kernel_prefix + 'epc17_2.hpp',
+    'LDA', 1e-24, 0.,
+    { 'a': '2.35',
+      'b': '2.40',
+      'c': '6.60' },
+    False, False, True 
+    ),
+
+  'EPC18_1' : GenMetaData( 'BuiltinEPC18_1', 
+    libxc_prefix + 'lda_exc/lda_c_epc18.c', 
+    kernel_prefix + 'epc18_1.hpp',
+    'LDA', 1e-24, 0.,
+    { 'a': '1.80',
+      'b': '0.10',
+      'c': '0.03' },
+    False, False, True 
+    ),
+
+  'EPC18_2' : GenMetaData( 'BuiltinEPC18_2', 
+    libxc_prefix + 'lda_exc/lda_c_epc18.c', 
+    kernel_prefix + 'epc18_2.hpp',
+    'LDA', 1e-24, 0.,
+    { 'a': '3.90',
+      'b': '0.50',
+      'c': '0.06' },
+    False, False, True 
+    ),
+
   'SlaterExchange' : GenMetaData( 'BuiltinSlaterExchange', 
     libxc_prefix + 'lda_exc/lda_x.c', 
     kernel_prefix + 'slater_exchange.hpp',
@@ -734,14 +775,15 @@ def __init__( self, local_name, libxc_file, ofname, xc_type, dens_tol, exx_coeff
   static constexpr bool is_mgga = {4};
   static constexpr bool needs_laplacian = {5};
   static constexpr bool is_kedf = {6};
+  static constexpr bool is_epc  = {7};
 
-  static constexpr double dens_tol  = {7};
+  static constexpr double dens_tol  = {8};
   static constexpr double zeta_tol  = 1e-15;
-  static constexpr double sigma_tol  = {8};
+  static constexpr double sigma_tol  = {9};
   static constexpr double tau_tol = is_kedf ? 0.0 : 1e-20;
 
-  static constexpr bool is_hyb  = {9};
-  static constexpr double exx_coeff = {10};
+  static constexpr bool is_hyb  = {10};
+  static constexpr double exx_coeff = {11};
 """
 
 lda_exc_args_unpolar     = "double rho, double& eps"
@@ -811,11 +853,13 @@ def __init__( self, local_name, libxc_file, ofname, xc_type, dens_tol, exx_coeff
   is_mgga = xc_type == 'MGGA'
   needs_laplacian = (xc_type == 'MGGA') and meta_data.needs_laplacian
   is_kedf = meta_data.is_kedf
+  is_epc  = meta_data.is_epc
 
   xc_struct_prefix = struct_prefix.format(
     meta_data.local_name, xc_type.lower(), str(is_lda).lower(), 
-    str(is_gga).lower(), str(is_mgga).lower(), str(needs_laplacian).lower(), str(is_kedf).lower(),
-    meta_data.dens_tol, meta_data.dens_tol**(4.0/3.0), str(meta_data.is_hyb).lower(), meta_data.exx_coeff )
+    str(is_gga).lower(), str(is_mgga).lower(), str(needs_laplacian).lower(), 
+    str(is_kedf).lower(), str(is_epc).lower(), meta_data.dens_tol, 
+    meta_data.dens_tol**(4.0/3.0), str(meta_data.is_hyb).lower(), meta_data.exx_coeff )
 
   xc_param_lines = []
   for pname, valstr in meta_data.params.items():

include/exchcxx/enums/functionals.hpp

@@ -59,7 +59,11 @@ enum class Functional {
   PBE0,
   SCAN,
   R2SCAN,
-  R2SCANL
+  R2SCANL,
+  EPC17_1,
+  EPC17_2,
+  EPC18_1,
+  EPC18_2,
 };
 
 extern BidirectionalMap<std::string, Functional> functional_map;

include/exchcxx/enums/kernels.hpp

@@ -101,6 +101,12 @@ enum class Kernel {
   // Hybrid GGA functionals
   B3LYP,
   PBE0,
+
+  // NEO LDA Functionals
+  EPC17_1,
+  EPC17_2,
+  EPC18_1,
+  EPC18_2,
 };
 
 extern BidirectionalMap<std::string, Kernel> kernel_map;

include/exchcxx/impl/builtin/fwd.hpp

@@ -88,6 +88,10 @@ struct BuiltinSCANL_C;
 struct BuiltinR2SCANL_X;
 struct BuiltinR2SCANL_C;
 
+struct BuiltinEPC17_1;
+struct BuiltinEPC17_2;
+struct BuiltinEPC18_1;
+struct BuiltinEPC18_2;
 
 template <typename KernelType>
 struct kernel_traits;

include/exchcxx/impl/builtin/interface.hpp

@@ -72,6 +72,7 @@ class BuiltinKernelInterface : public XCKernelImpl {
   bool is_gga_()       const noexcept override;
   bool is_mgga_()      const noexcept override;
   bool is_hyb_()       const noexcept override;
+  bool is_epc_()       const noexcept override;
   bool needs_laplacian_()       const noexcept override;
   bool needs_tau_()    const noexcept override;
   bool is_polarized_() const noexcept override;

include/exchcxx/impl/builtin/kernel_type.hpp

@@ -71,6 +71,7 @@ class BuiltinKernel {
   virtual bool is_gga()       const noexcept = 0;
   virtual bool is_mgga()      const noexcept = 0;
   virtual bool is_hyb()       const noexcept = 0;
+  virtual bool is_epc()       const noexcept = 0;
   virtual bool needs_laplacian()       const noexcept = 0;
   virtual bool needs_tau()    const noexcept = 0;
   virtual double hyb_exx()    const noexcept = 0;
@@ -375,6 +376,7 @@ struct BuiltinKernelImpl<
   inline bool is_lda()  const noexcept override { return traits::is_lda;  }
   inline bool is_gga()  const noexcept override { return traits::is_gga;  }
   inline bool is_mgga() const noexcept override { return traits::is_mgga; }
+  inline bool is_epc()  const noexcept override { return traits::is_epc;  }
 
   inline double hyb_exx() const noexcept override {
     return traits::is_hyb ? traits::exx_coeff : 0.;
@@ -525,6 +527,7 @@ struct BuiltinKernelImpl<
   inline bool is_lda()  const noexcept override { return traits::is_lda;  }
   inline bool is_gga()  const noexcept override { return traits::is_gga;  }
   inline bool is_mgga() const noexcept override { return traits::is_mgga; }
+  inline bool is_epc()  const noexcept override { return traits::is_epc;  }
 
   inline double hyb_exx() const noexcept override {
     return traits::is_hyb ? traits::exx_coeff : 0.;
@@ -676,6 +679,7 @@ struct BuiltinKernelImpl<
   inline bool is_lda()  const noexcept override { return traits::is_lda;  }
   inline bool is_gga()  const noexcept override { return traits::is_gga;  }
   inline bool is_mgga() const noexcept override { return traits::is_mgga; }
+  inline bool is_epc()  const noexcept override { return traits::is_epc;  }
 
   inline double hyb_exx() const noexcept override {
     return traits::is_hyb ? traits::exx_coeff : 0.;

include/exchcxx/impl/builtin/kernels.hpp

@@ -81,4 +81,8 @@
 #include <exchcxx/impl/builtin/kernels/pc07_k.hpp>
 #include <exchcxx/impl/builtin/kernels/pc07opt_k.hpp>
 
+#include <exchcxx/impl/builtin/kernels/epc17_1.hpp>
+#include <exchcxx/impl/builtin/kernels/epc17_2.hpp>
+#include <exchcxx/impl/builtin/kernels/epc18_1.hpp>
+#include <exchcxx/impl/builtin/kernels/epc18_2.hpp>
 

include/exchcxx/impl/builtin/kernels/b3lyp.hpp

@@ -20,6 +20,7 @@ struct kernel_traits<BuiltinB3LYP> {
   static constexpr bool is_lda  = false;
   static constexpr bool is_gga  = true;
   static constexpr bool is_mgga = false;
+  static constexpr bool is_epc  = false;
   static constexpr double exx_coeff = 0.20;
 
   static constexpr double b3lyp_ax = 0.72; // % GGA X

include/exchcxx/impl/builtin/kernels/b88.hpp

@@ -21,6 +21,7 @@ struct kernel_traits< BuiltinB88 > :
   static constexpr bool is_mgga = false;
   static constexpr bool needs_laplacian = false;
   static constexpr bool is_kedf = false;
+  static constexpr bool is_epc  = false;
 
   static constexpr double dens_tol  = 1e-25;
   static constexpr double zeta_tol  = 1e-15;
@@ -391,4 +392,4 @@ struct BuiltinB88 : detail::BuiltinKernelImpl< BuiltinB88 > {
 
 
 
-} // namespace ExchCXX
+} // namespace ExchCXX

include/exchcxx/impl/builtin/kernels/deorbitalized.hpp

@@ -18,6 +18,7 @@ struct kernel_traits<Deorbitalized<XCEF,KEDF>> {
   static constexpr bool is_mgga = true;
   static constexpr bool needs_laplacian = true;
   static constexpr bool is_kedf = false;
+  static constexpr bool is_epc  = false;
   static constexpr double exx_coeff = xc_traits::exx_coeff + ke_traits::exx_coeff;
 
   BUILTIN_KERNEL_EVAL_RETURN