diff --git a/psi4/src/psi4/cc/ccdensity/Gijab_RHF.cc b/psi4/src/psi4/cc/ccdensity/Gijab_RHF.cc
index 7a182a00adb..3ccc77b7276 100644
--- a/psi4/src/psi4/cc/ccdensity/Gijab_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/Gijab_RHF.cc
@@ -30,7 +30,7 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/ccdensity/add_ref_RHF.cc b/psi4/src/psi4/cc/ccdensity/add_ref_RHF.cc
index b66d2237194..341ed163ae7 100644
--- a/psi4/src/psi4/cc/ccdensity/add_ref_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/add_ref_RHF.cc
@@ -30,7 +30,7 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libiwl/iwl.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/ccdensity/build_Z_RHF.cc b/psi4/src/psi4/cc/ccdensity/build_Z_RHF.cc
index fc9aabd31a3..8a2cab21172 100644
--- a/psi4/src/psi4/cc/ccdensity/build_Z_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/build_Z_RHF.cc
@@ -30,11 +30,11 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdlib.h>
+#include <cstdlib>
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
 #include "psi4/libciomr/libciomr.h"
-#include <math.h>
+#include <cmath>
 #include "MOInfo.h"
 #include "Params.h"
 #include "Frozen.h"
diff --git a/psi4/src/psi4/cc/ccdensity/deanti_RHF.cc b/psi4/src/psi4/cc/ccdensity/deanti_RHF.cc
index c369a11b1f4..c16e8e80a79 100644
--- a/psi4/src/psi4/cc/ccdensity/deanti_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/deanti_RHF.cc
@@ -40,7 +40,7 @@
 #define EXTERN
 #include "globals.h"
 
-#include <stdio.h>
+#include <cstdio>
 
 namespace psi {
 namespace ccdensity {
diff --git a/psi4/src/psi4/cc/ccdensity/dump_RHF.cc b/psi4/src/psi4/cc/ccdensity/dump_RHF.cc
index faca5b2197d..6c78502765e 100644
--- a/psi4/src/psi4/cc/ccdensity/dump_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/dump_RHF.cc
@@ -30,7 +30,7 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libciomr/libciomr.h"
 #include "psi4/libiwl/iwl.h"
 #include "psi4/libdpd/dpd.h"
diff --git a/psi4/src/psi4/cc/ccdensity/energy_RHF.cc b/psi4/src/psi4/cc/ccdensity/energy_RHF.cc
index 0db89e67f6a..fb9c4cecdb9 100644
--- a/psi4/src/psi4/cc/ccdensity/energy_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/energy_RHF.cc
@@ -31,7 +31,7 @@
     \brief Calculates the one- and two-electron CC energies using the
     coresponding one- and two-particle density matrices.
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/ccdensity/energy_ROHF.cc b/psi4/src/psi4/cc/ccdensity/energy_ROHF.cc
index ce0a2c487cb..c556d71dd31 100644
--- a/psi4/src/psi4/cc/ccdensity/energy_ROHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/energy_ROHF.cc
@@ -31,7 +31,7 @@
     \brief  Calculates the one- and two-electron CC energies using the
     coresponding one- and two-particle density matrices.
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/ccdensity/energy_UHF.cc b/psi4/src/psi4/cc/ccdensity/energy_UHF.cc
index 8104879726e..0437fb16aba 100644
--- a/psi4/src/psi4/cc/ccdensity/energy_UHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/energy_UHF.cc
@@ -31,7 +31,7 @@
     \brief Calculates the one- and two-electron CC energies using the
     coresponding one- and two-particle density matrices.
 */
-#include <stdio.h>
+#include <cstdio>
 #include <cstring>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/cc/ccdensity/fold_RHF.cc b/psi4/src/psi4/cc/ccdensity/fold_RHF.cc
index 0eaa0553ad2..bc654e78a0d 100644
--- a/psi4/src/psi4/cc/ccdensity/fold_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/fold_RHF.cc
@@ -30,7 +30,7 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/ccdensity/sortI_RHF.cc b/psi4/src/psi4/cc/ccdensity/sortI_RHF.cc
index 6c833c8a7f7..9ea37dc4956 100644
--- a/psi4/src/psi4/cc/ccdensity/sortI_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/sortI_RHF.cc
@@ -30,9 +30,9 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libdpd/dpd.h"
-#include <math.h>
+#include <cmath>
 #include "psi4/libciomr/libciomr.h"
 #include "psi4/libiwl/iwl.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/cc/ccdensity/sortone_RHF.cc b/psi4/src/psi4/cc/ccdensity/sortone_RHF.cc
index 479cad14b33..4e474bff2c1 100644
--- a/psi4/src/psi4/cc/ccdensity/sortone_RHF.cc
+++ b/psi4/src/psi4/cc/ccdensity/sortone_RHF.cc
@@ -30,9 +30,9 @@
     \ingroup CCDENSITY
     \brief Enter brief description of file here
 */
-#include <stdio.h>
+#include <cstdio>
 #include "psi4/libdpd/dpd.h"
-#include <math.h>
+#include <cmath>
 #include "psi4/libciomr/libciomr.h"
 #include "psi4/libpsio/psio.h"
 #include "psi4/libiwl/iwl.h"
diff --git a/psi4/src/psi4/cc/ccdensity/x_xi2.cc b/psi4/src/psi4/cc/ccdensity/x_xi2.cc
index d3112d15ec9..14e49f5f7a0 100644
--- a/psi4/src/psi4/cc/ccdensity/x_xi2.cc
+++ b/psi4/src/psi4/cc/ccdensity/x_xi2.cc
@@ -32,7 +32,7 @@
 */
 #include <cstdio>
 #include "psi4/libdpd/dpd.h"
-#include "math.h"
+#include <cmath>
 #include "MOInfo.h"
 #include "Params.h"
 #include "Frozen.h"
diff --git a/psi4/src/psi4/cc/ccdensity/x_xi2_rhf.cc b/psi4/src/psi4/cc/ccdensity/x_xi2_rhf.cc
index 4d49742dc55..00aaf59dc8a 100644
--- a/psi4/src/psi4/cc/ccdensity/x_xi2_rhf.cc
+++ b/psi4/src/psi4/cc/ccdensity/x_xi2_rhf.cc
@@ -32,7 +32,7 @@
 */
 #include <cstdio>
 #include "psi4/libdpd/dpd.h"
-#include "math.h"
+#include <cmath>
 #include "MOInfo.h"
 #include "Params.h"
 #include "Frozen.h"
diff --git a/psi4/src/psi4/cc/ccdensity/x_xi2_uhf.cc b/psi4/src/psi4/cc/ccdensity/x_xi2_uhf.cc
index 29a530c842e..9f3cdb23c41 100644
--- a/psi4/src/psi4/cc/ccdensity/x_xi2_uhf.cc
+++ b/psi4/src/psi4/cc/ccdensity/x_xi2_uhf.cc
@@ -32,7 +32,7 @@
 */
 #include <cstdio>
 #include "psi4/libdpd/dpd.h"
-#include "math.h"
+#include <cmath>
 #include "MOInfo.h"
 #include "Params.h"
 #include "Frozen.h"
diff --git a/psi4/src/psi4/cc/cchbar/Wamef.cc b/psi4/src/psi4/cc/cchbar/Wamef.cc
index 93f14f05dc6..76dfa19eb15 100644
--- a/psi4/src/psi4/cc/cchbar/Wamef.cc
+++ b/psi4/src/psi4/cc/cchbar/Wamef.cc
@@ -31,7 +31,7 @@
     \brief Enter brief description of file here
 */
 #include <cstdio>
-#include <math.h>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/cc/cchbar/Wmbej.cc b/psi4/src/psi4/cc/cchbar/Wmbej.cc
index 242a84fbd4a..b95e6b54c99 100644
--- a/psi4/src/psi4/cc/cchbar/Wmbej.cc
+++ b/psi4/src/psi4/cc/cchbar/Wmbej.cc
@@ -31,7 +31,7 @@
     \brief Enter brief description of file here
 */
 #include <cstdio>
-#include <math.h>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/cc/cchbar/Wmbij.cc b/psi4/src/psi4/cc/cchbar/Wmbij.cc
index f21d76faf8b..61d8b2ca970 100644
--- a/psi4/src/psi4/cc/cchbar/Wmbij.cc
+++ b/psi4/src/psi4/cc/cchbar/Wmbij.cc
@@ -31,7 +31,7 @@
     \brief Enter brief description of file here
 */
 #include <cstdio>
-#include <math.h>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/cchbar/Wmnie.cc b/psi4/src/psi4/cc/cchbar/Wmnie.cc
index d0d0ea0948a..3ffa690d1da 100644
--- a/psi4/src/psi4/cc/cchbar/Wmnie.cc
+++ b/psi4/src/psi4/cc/cchbar/Wmnie.cc
@@ -31,7 +31,7 @@
     \brief Enter brief description of file here
 */
 #include <cstdio>
-#include <math.h>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "MOInfo.h"
 #include "Params.h"
diff --git a/psi4/src/psi4/cc/cclambda/L1.cc b/psi4/src/psi4/cc/cclambda/L1.cc
index bc9472d9597..77ca7b01619 100644
--- a/psi4/src/psi4/cc/cclambda/L1.cc
+++ b/psi4/src/psi4/cc/cclambda/L1.cc
@@ -30,8 +30,8 @@
     \ingroup CCLAMBDA
     \brief Enter brief description of file here
 */
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <string>
 #include <cstring>
 #include "psi4/libdpd/dpd.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_UHF_AAA.cc b/psi4/src/psi4/cc/cctriples/T3_UHF_AAA.cc
index 903edd950b9..bc977fd1982 100644
--- a/psi4/src/psi4/cc/cctriples/T3_UHF_AAA.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_UHF_AAA.cc
@@ -103,10 +103,10 @@
 ** Modified to return disconnected triples, TDC, Feburary 2008
 */
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <cstring>
-#include <math.h>
+#include <cmath>
 #include "psi4/libqt/qt.h"
 #include "psi4/libdpd/dpd.h"
 #include "psi4/psifiles.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_UHF_AAB.cc b/psi4/src/psi4/cc/cctriples/T3_UHF_AAB.cc
index 72062481671..8e0cd9bb3e1 100644
--- a/psi4/src/psi4/cc/cctriples/T3_UHF_AAB.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_UHF_AAB.cc
@@ -101,10 +101,10 @@
 ** TDC, July 2004
 */
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <cstring>
-#include <math.h>
+#include <cmath>
 #include "psi4/libqt/qt.h"
 #include "psi4/libdpd/dpd.h"
 #include "psi4/psifiles.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_UHF_ABC.cc b/psi4/src/psi4/cc/cctriples/T3_UHF_ABC.cc
index 1acf01fd689..d24e49358dc 100644
--- a/psi4/src/psi4/cc/cctriples/T3_UHF_ABC.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_UHF_ABC.cc
@@ -26,10 +26,10 @@
  * @END LICENSE
  */
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <cstring>
-#include <math.h>
+#include <cmath>
 #include "psi4/libqt/qt.h"
 #include "psi4/libdpd/dpd.h"
 #include "psi4/psifiles.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_grad_RHF.cc b/psi4/src/psi4/cc/cctriples/T3_grad_RHF.cc
index de90f2ed193..d7bd1c9a206 100644
--- a/psi4/src/psi4/cc/cctriples/T3_grad_RHF.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_grad_RHF.cc
@@ -31,9 +31,9 @@
     \brief Computes T3-dependent terms needed in cclambda and
     ccdensity for (T) contributions to the CCSD(T) energy gradient.
 */
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
 #include "psi4/libciomr/libciomr.h"
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAA.cc b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAA.cc
index fdd96960481..195038727af 100644
--- a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAA.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAA.cc
@@ -30,9 +30,9 @@
     \ingroup CCTRIPLES
     \brief Enter brief description of file here
 */
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAB.cc b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAB.cc
index 6530c6460b6..ff6cc6afb31 100644
--- a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAB.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_AAB.cc
@@ -30,9 +30,9 @@
     \ingroup CCTRIPLES
     \brief Enter brief description of file here
 */
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
 #include "psi4/libciomr/libciomr.h"
 #include "psi4/libqt/qt.h"
 #include "psi4/libdpd/dpd.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBA.cc b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBA.cc
index 8671ae5725c..5dee1ca8f60 100644
--- a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBA.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBA.cc
@@ -30,9 +30,9 @@
     \ingroup CCTRIPLES
     \brief Enter brief description of file here
 */
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBB.cc b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBB.cc
index 400b16130d7..dd792093370 100644
--- a/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBB.cc
+++ b/psi4/src/psi4/cc/cctriples/T3_grad_UHF_BBB.cc
@@ -30,9 +30,9 @@
     \ingroup CCTRIPLES
     \brief Enter brief description of file here
 */
-#include <stdio.h>
-#include <stdlib.h>
-#include <math.h>
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
 #include "psi4/libdpd/dpd.h"
 #include "psi4/libqt/qt.h"
 #include "MOInfo.h"
diff --git a/psi4/src/psi4/dcft/main.cc b/psi4/src/psi4/dcft/main.cc
index b0930623723..bcff09da026 100644
--- a/psi4/src/psi4/dcft/main.cc
+++ b/psi4/src/psi4/dcft/main.cc
@@ -35,8 +35,8 @@
 #include "psi4/libpsi4util/PsiOutStream.h"
 #include "psi4/liboptions/liboptions.h"
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/detci/slaterd.h b/psi4/src/psi4/detci/slaterd.h
index 205d19800db..8195180aeda 100644
--- a/psi4/src/psi4/detci/slaterd.h
+++ b/psi4/src/psi4/detci/slaterd.h
@@ -58,7 +58,7 @@
 #ifndef _psi_src_bin_detci_slaterd_h
 #define _psi_src_bin_detci_slaterd_h
 
-#include <stdlib.h>
+#include <cstdlib>
 #include <string>
 
 namespace psi {
diff --git a/psi4/src/psi4/dfocc/ekt.cc b/psi4/src/psi4/dfocc/ekt.cc
index 8893cb63cbe..801c9240710 100644
--- a/psi4/src/psi4/dfocc/ekt.cc
+++ b/psi4/src/psi4/dfocc/ekt.cc
@@ -27,7 +27,7 @@
  */
 
 // Latest revision on April 38, 2013.
-#include <stdio.h>
+#include <cstdio>
 #include <fstream>
 #include <cmath>
 #include "ekt.h"
diff --git a/psi4/src/psi4/dfocc/tensors.cc b/psi4/src/psi4/dfocc/tensors.cc
index 68ffd737180..33d3389f47d 100644
--- a/psi4/src/psi4/dfocc/tensors.cc
+++ b/psi4/src/psi4/dfocc/tensors.cc
@@ -27,7 +27,7 @@
  */
 
 // Latest revision on April 38, 2013.
-#include <stdio.h>
+#include <cstdio>
 #include <fstream>
 #include <cmath>
 #include "psi4/libqt/qt.h"
diff --git a/psi4/src/psi4/fnocc/blas.cc b/psi4/src/psi4/fnocc/blas.cc
index 8841d76e1a7..a3fca416982 100644
--- a/psi4/src/psi4/fnocc/blas.cc
+++ b/psi4/src/psi4/fnocc/blas.cc
@@ -27,7 +27,7 @@
  */
 
 #include "blas.h"
-#include <stdlib.h>
+#include <cstdlib>
 
 #include "psi4/pragma.h"
 
diff --git a/psi4/src/psi4/lib3index/cholesky.cc b/psi4/src/psi4/lib3index/cholesky.cc
index 45aa4c38784..8b5e3a67ed7 100644
--- a/psi4/src/psi4/lib3index/cholesky.cc
+++ b/psi4/src/psi4/lib3index/cholesky.cc
@@ -32,7 +32,7 @@ PRAGMA_WARNING_IGNORE_DEPRECATED_DECLARATIONS
 #include <memory>
 PRAGMA_WARNING_POP
 #include "psi4/libqt/qt.h"
-#include <math.h>
+#include <cmath>
 #include <limits>
 #include <vector>
 #include "cholesky.h"
diff --git a/psi4/src/psi4/lib3index/dftensor.cc b/psi4/src/psi4/lib3index/dftensor.cc
index 15623119a3d..433db25ef6f 100644
--- a/psi4/src/psi4/lib3index/dftensor.cc
+++ b/psi4/src/psi4/lib3index/dftensor.cc
@@ -37,7 +37,7 @@
 #include <fstream>
 #include <algorithm>
 #include <utility>
-#include <ctype.h>
+#include <cctype>
 #include "psi4/libmints/matrix.h"
 #include "psi4/libmints/mintshelper.h"
 #include "psi4/libmints/basisset.h"
diff --git a/psi4/src/psi4/libdiis/diisentry.cc b/psi4/src/psi4/libdiis/diisentry.cc
index 556c5dabbf3..22aa43ab17f 100644
--- a/psi4/src/psi4/libdiis/diisentry.cc
+++ b/psi4/src/psi4/libdiis/diisentry.cc
@@ -32,7 +32,7 @@ PRAGMA_WARNING_IGNORE_DEPRECATED_DECLARATIONS
 PRAGMA_WARNING_POP
 #include "psi4/libpsio/psio.hpp"
 #include "diisentry.h"
-#include <math.h>
+#include <cmath>
 #include "psi4/libqt/qt.h"
 #include "psi4/psifiles.h"
 #include <sstream>
diff --git a/psi4/src/psi4/libdisp/dispersion.cc b/psi4/src/psi4/libdisp/dispersion.cc
index 8845fd4a6f6..223b3c387f2 100644
--- a/psi4/src/psi4/libdisp/dispersion.cc
+++ b/psi4/src/psi4/libdisp/dispersion.cc
@@ -46,7 +46,7 @@
 
 #include <iostream>
 #include <iomanip>
-#include <stdlib.h>
+#include <cstdlib>
 #include <string>
 #include <sstream>
 #include <vector>
diff --git a/psi4/src/psi4/libfilesystem/path.cc b/psi4/src/psi4/libfilesystem/path.cc
index c3063ea3ca7..ca21aded98c 100644
--- a/psi4/src/psi4/libfilesystem/path.cc
+++ b/psi4/src/psi4/libfilesystem/path.cc
@@ -69,7 +69,7 @@ static int SYSTEM_TRUNCATE(const char *path, off_t length) {
 #define PATH_SEPARATOR "/"
 #endif
 #include <sys/stat.h>
-#include <limits.h>
+#include <climits>
 
 namespace psi {
 namespace filesystem {
diff --git a/psi4/src/psi4/libfock/cubature.cc b/psi4/src/psi4/libfock/cubature.cc
index f7ce15a41ec..16c41eb02b1 100644
--- a/psi4/src/psi4/libfock/cubature.cc
+++ b/psi4/src/psi4/libfock/cubature.cc
@@ -46,8 +46,8 @@
 #include <sstream>
 #include <cstdio>
 #include <limits>
-#include <ctype.h>
-#include <assert.h>
+#include <cctype>
+#include <cassert>
 
 #ifdef _OPENMP
 #include <omp.h>
diff --git a/psi4/src/psi4/libmints/chartab.cc b/psi4/src/psi4/libmints/chartab.cc
index b313c04cf3d..9b0cf582eaa 100644
--- a/psi4/src/psi4/libmints/chartab.cc
+++ b/psi4/src/psi4/libmints/chartab.cc
@@ -82,7 +82,7 @@
 #include "psi4/psi4-dec.h"
 #include "psi4/libpsi4util/exception.h"
 
-#include <ctype.h>
+#include <cctype>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/libmints/deriv.cc b/psi4/src/psi4/libmints/deriv.cc
index fb44557cd8e..0c557afbd7c 100644
--- a/psi4/src/psi4/libmints/deriv.cc
+++ b/psi4/src/psi4/libmints/deriv.cc
@@ -46,8 +46,8 @@
 #include "psi4/libpsi4util/PsiOutStream.h"
 #include "psi4/libpsi4util/process.h"
 
-#include <stdio.h>
-#include <stdlib.h>
+#include <cstdio>
+#include <cstdlib>
 #include <string>
 #include <memory>
 #include <array>
diff --git a/psi4/src/psi4/libmints/intvector.cc b/psi4/src/psi4/libmints/intvector.cc
index 1f948586018..b46a13eda44 100644
--- a/psi4/src/psi4/libmints/intvector.cc
+++ b/psi4/src/psi4/libmints/intvector.cc
@@ -27,7 +27,7 @@
  */
 
 #include <cstdlib>
-#include <string.h>
+#include <cstring>
 #include "psi4/libqt/qt.h"
 #include "matrix.h"
 #include "vector.h"
diff --git a/psi4/src/psi4/libmints/irrep.cc b/psi4/src/psi4/libmints/irrep.cc
index 51d245509cd..c4d25d95cf7 100644
--- a/psi4/src/psi4/libmints/irrep.cc
+++ b/psi4/src/psi4/libmints/irrep.cc
@@ -78,7 +78,7 @@
 #include "psi4/libmints/pointgrp.h"
 #include "psi4/libpsi4util/PsiOutStream.h"
 
-#include <stdlib.h>
+#include <cstdlib>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/libmints/petitelist.h b/psi4/src/psi4/libmints/petitelist.h
index 48286a09545..b165834f318 100644
--- a/psi4/src/psi4/libmints/petitelist.h
+++ b/psi4/src/psi4/libmints/petitelist.h
@@ -34,7 +34,7 @@
 
 #include <map>
 #include <cstdio>
-#include <stdint.h>
+#include <cstdint>
 
 #include "psi4/pragma.h"
 PRAGMA_WARNING_PUSH
diff --git a/psi4/src/psi4/libmints/pointgrp.cc b/psi4/src/psi4/libmints/pointgrp.cc
index f29986d2816..62c2961295a 100644
--- a/psi4/src/psi4/libmints/pointgrp.cc
+++ b/psi4/src/psi4/libmints/pointgrp.cc
@@ -85,7 +85,7 @@
 
 #include <cstdlib>
 #include <cstring>
-#include <ctype.h>
+#include <cctype>
 #include <cmath>
 
 namespace psi {
diff --git a/psi4/src/psi4/libmints/pointgrp.h b/psi4/src/psi4/libmints/pointgrp.h
index beba5e44294..0f93e383e98 100644
--- a/psi4/src/psi4/libmints/pointgrp.h
+++ b/psi4/src/psi4/libmints/pointgrp.h
@@ -83,9 +83,9 @@
 #include "psi4/libmints/vector3.h"
 #include "psi4/psi4-dec.h"
 
-#include <string.h>
+#include <cstring>
 #include <cstdio>
-#include <stdint.h>
+#include <cstdint>
 #include <vector>
 #include <map>
 
diff --git a/psi4/src/psi4/libmints/solidharmonics.cc b/psi4/src/psi4/libmints/solidharmonics.cc
index 2eb9b703af5..1afb41edebb 100644
--- a/psi4/src/psi4/libmints/solidharmonics.cc
+++ b/psi4/src/psi4/libmints/solidharmonics.cc
@@ -29,7 +29,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <cmath>
-#include <stdint.h>
+#include <cstdint>
 
 #include "matrix.h"
 #include "integral.h"
diff --git a/psi4/src/psi4/libmints/vector.cc b/psi4/src/psi4/libmints/vector.cc
index 47cf6b3def0..0280d88b867 100644
--- a/psi4/src/psi4/libmints/vector.cc
+++ b/psi4/src/psi4/libmints/vector.cc
@@ -35,8 +35,8 @@
 #include <algorithm>
 #include <numeric>
 #include <cstdlib>
-#include <string.h>
-#include <math.h>
+#include <cstring>
+#include <cmath>
 
 namespace psi {
 
diff --git a/psi4/src/psi4/libmints/wavefunction.h b/psi4/src/psi4/libmints/wavefunction.h
index 9e7b8ffed4a..47e4e3bfc2c 100644
--- a/psi4/src/psi4/libmints/wavefunction.h
+++ b/psi4/src/psi4/libmints/wavefunction.h
@@ -33,7 +33,7 @@
 #include "psi4/libpsi4util/exception.h"
 #include "psi4/libmints/dimension.h"
 
-#include <stddef.h>
+#include <cstddef>
 #include <vector>
 #include <array>
 #include <memory>
diff --git a/psi4/src/psi4/liboptions/liboptions.cc b/psi4/src/psi4/liboptions/liboptions.cc
index 35cca140a02..c1c46157b1c 100644
--- a/psi4/src/psi4/liboptions/liboptions.cc
+++ b/psi4/src/psi4/liboptions/liboptions.cc
@@ -36,7 +36,7 @@
 #include <iomanip>
 #include <sstream>
 #include <numeric>
-#include <assert.h>
+#include <cassert>
 
 #include "liboptions.h"
 #include "liboptions_python.h"
diff --git a/psi4/src/psi4/liboptions/print.cc b/psi4/src/psi4/liboptions/print.cc
index c7ee7e03ee5..843c6bed855 100644
--- a/psi4/src/psi4/liboptions/print.cc
+++ b/psi4/src/psi4/liboptions/print.cc
@@ -36,7 +36,7 @@
 #include <iomanip>
 #include <sstream>
 #include <algorithm>
-#include <assert.h>
+#include <cassert>
 #include "psi4/pragma.h"
 PRAGMA_WARNING_PUSH
 PRAGMA_WARNING_IGNORE_DEPRECATED_DECLARATIONS
diff --git a/psi4/src/psi4/libpsi4util/exception.h b/psi4/src/psi4/libpsi4util/exception.h
index d0883aba84d..6b67ccceefd 100644
--- a/psi4/src/psi4/libpsi4util/exception.h
+++ b/psi4/src/psi4/libpsi4util/exception.h
@@ -33,7 +33,7 @@
 #include <exception>
 #include <stdexcept>
 #include <sstream>
-#include <string.h>
+#include <cstring>
 
 #if defined(__GNUC__) || (defined(__ICC) && (__ICC >= 600))
 #define PSI4_CURRENT_FUNCTION __PRETTY_FUNCTION__
diff --git a/psi4/src/psi4/libpsi4util/stl_string.cc b/psi4/src/psi4/libpsi4util/stl_string.cc
index 49be6d4efcd..f014600dbaf 100644
--- a/psi4/src/psi4/libpsi4util/stl_string.cc
+++ b/psi4/src/psi4/libpsi4util/stl_string.cc
@@ -32,11 +32,11 @@
 #include <algorithm>
 #include <cstdio>
 #include <sstream>
-#include <string.h>
+#include <cstring>
 #include <regex>
 #include <sys/types.h>
 #include <sys/stat.h>
-#include <limits.h>
+#include <climits>
 
 #include "libpsi4util.h"
 
diff --git a/psi4/src/psi4/libqt/blas_intfc.cc b/psi4/src/psi4/libqt/blas_intfc.cc
index 9ba67680080..c59c3a0a993 100644
--- a/psi4/src/psi4/libqt/blas_intfc.cc
+++ b/psi4/src/psi4/libqt/blas_intfc.cc
@@ -51,7 +51,7 @@
 */
 
 #include <cstdio>
-#include <limits.h>
+#include <climits>
 #include <cmath>
 
 #include "psi4/pragma.h"
diff --git a/psi4/src/psi4/libqt/dx_write.cc b/psi4/src/psi4/libqt/dx_write.cc
index 624f55710cf..8645826bcf6 100644
--- a/psi4/src/psi4/libqt/dx_write.cc
+++ b/psi4/src/psi4/libqt/dx_write.cc
@@ -26,8 +26,8 @@
  * @END LICENSE
  */
 
-#include <stdio.h>
-#include <math.h>
+#include <cstdio>
+#include <cmath>
 #include "psi4/psi4-dec.h"
 
 #include "psi4/libciomr/libciomr.h"
diff --git a/psi4/src/psi4/libsapt_solver/sapt2p3.cc b/psi4/src/psi4/libsapt_solver/sapt2p3.cc
index 221f6fb6c6b..cf84923c284 100644
--- a/psi4/src/psi4/libsapt_solver/sapt2p3.cc
+++ b/psi4/src/psi4/libsapt_solver/sapt2p3.cc
@@ -28,7 +28,7 @@
 
 #include "sapt2p3.h"
 #include "psi4/physconst.h"
-#include <math.h>
+#include <cmath>
 
 namespace psi {
 namespace sapt {
diff --git a/psi4/src/psi4/libscf_solver/cuhf.cc b/psi4/src/psi4/libscf_solver/cuhf.cc
index e3f49516331..4899ccb3f3d 100644
--- a/psi4/src/psi4/libscf_solver/cuhf.cc
+++ b/psi4/src/psi4/libscf_solver/cuhf.cc
@@ -42,9 +42,9 @@
 #include "psi4/libdiis/diismanager.h"
 #include "psi4/libdiis/diisentry.h"
 
-#include <stdlib.h>
-#include <stdio.h>
-#include <math.h>
+#include <cstdlib>
+#include <cstdio>
+#include <cmath>
 #include <algorithm>
 #include <vector>
 #include <utility>
diff --git a/psi4/src/psi4/libscf_solver/rohf.cc b/psi4/src/psi4/libscf_solver/rohf.cc
index c7225bf7bff..ce93b52525d 100644
--- a/psi4/src/psi4/libscf_solver/rohf.cc
+++ b/psi4/src/psi4/libscf_solver/rohf.cc
@@ -27,9 +27,9 @@
  */
 
 #include <ctime>
-#include <stdlib.h>
-#include <stdio.h>
-#include <math.h>
+#include <cstdlib>
+#include <cstdio>
+#include <cmath>
 #include <algorithm>
 #include <vector>
 #include <utility>
diff --git a/psi4/src/psi4/libscf_solver/uhf.cc b/psi4/src/psi4/libscf_solver/uhf.cc
index 0559ca9921d..415f0e98b1d 100644
--- a/psi4/src/psi4/libscf_solver/uhf.cc
+++ b/psi4/src/psi4/libscf_solver/uhf.cc
@@ -27,9 +27,9 @@
  */
 
 #include <ctime>
-#include <stdlib.h>
-#include <stdio.h>
-#include <math.h>
+#include <cstdlib>
+#include <cstdio>
+#include <cmath>
 #include <algorithm>
 #include <functional>
 #include <vector>
diff --git a/psi4/src/psi4/libtrans/integraltransform_tei.cc b/psi4/src/psi4/libtrans/integraltransform_tei.cc
index e671d683fa7..e893769a2b8 100644
--- a/psi4/src/psi4/libtrans/integraltransform_tei.cc
+++ b/psi4/src/psi4/libtrans/integraltransform_tei.cc
@@ -31,9 +31,9 @@
 #include "psi4/libciomr/libciomr.h"
 #include "psi4/libiwl/iwl.hpp"
 #include "psi4/libqt/qt.h"
-#include <math.h>
-#include <ctype.h>
-#include <stdio.h>
+#include <cmath>
+#include <cctype>
+#include <cstdio>
 #include "psi4/psifiles.h"
 #include "mospace.h"
 
diff --git a/psi4/src/psi4/libtrans/integraltransform_tei_1st_half.cc b/psi4/src/psi4/libtrans/integraltransform_tei_1st_half.cc
index 2a09370794e..40467d8753d 100644
--- a/psi4/src/psi4/libtrans/integraltransform_tei_1st_half.cc
+++ b/psi4/src/psi4/libtrans/integraltransform_tei_1st_half.cc
@@ -38,9 +38,9 @@
 #include "psi4/psifiles.h"
 #include "psi4/libdpd/dpd.h"
 
-#include <math.h>
-#include <ctype.h>
-#include <stdio.h>
+#include <cmath>
+#include <cctype>
+#include <cstdio>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/libtrans/integraltransform_tei_2nd_half.cc b/psi4/src/psi4/libtrans/integraltransform_tei_2nd_half.cc
index 1546411c89e..e3874c9f628 100644
--- a/psi4/src/psi4/libtrans/integraltransform_tei_2nd_half.cc
+++ b/psi4/src/psi4/libtrans/integraltransform_tei_2nd_half.cc
@@ -38,9 +38,9 @@
 #include "psi4/psifiles.h"
 #include "psi4/libdpd/dpd.h"
 
-#include <math.h>
-#include <ctype.h>
-#include <stdio.h>
+#include <cmath>
+#include <cctype>
+#include <cstdio>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/libtrans/integraltransform_tpdm.cc b/psi4/src/psi4/libtrans/integraltransform_tpdm.cc
index 41faca1b82a..193c016ae82 100644
--- a/psi4/src/psi4/libtrans/integraltransform_tpdm.cc
+++ b/psi4/src/psi4/libtrans/integraltransform_tpdm.cc
@@ -37,9 +37,9 @@
 #include "psi4/libpsi4util/PsiOutStream.h"
 #include "psi4/psifiles.h"
 
-#include <math.h>
-#include <ctype.h>
-#include <stdio.h>
+#include <cmath>
+#include <cctype>
+#include <cstdio>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/libtrans/integraltransform_tpdm_restricted.cc b/psi4/src/psi4/libtrans/integraltransform_tpdm_restricted.cc
index c41a1b5a1f3..3c0bd021256 100644
--- a/psi4/src/psi4/libtrans/integraltransform_tpdm_restricted.cc
+++ b/psi4/src/psi4/libtrans/integraltransform_tpdm_restricted.cc
@@ -38,9 +38,9 @@
 #include "psi4/psifiles.h"
 #include "psi4/libdpd/dpd.h"
 
-#include <math.h>
-#include <ctype.h>
-#include <stdio.h>
+#include <cmath>
+#include <cctype>
+#include <cstdio>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/libtrans/integraltransform_tpdm_unrestricted.cc b/psi4/src/psi4/libtrans/integraltransform_tpdm_unrestricted.cc
index 10a4a0096a0..39b76cbcde5 100644
--- a/psi4/src/psi4/libtrans/integraltransform_tpdm_unrestricted.cc
+++ b/psi4/src/psi4/libtrans/integraltransform_tpdm_unrestricted.cc
@@ -38,9 +38,9 @@
 #include "psi4/psifiles.h"
 #include "psi4/libdpd/dpd.h"
 
-#include <math.h>
-#include <ctype.h>
-#include <stdio.h>
+#include <cmath>
+#include <cctype>
+#include <cstdio>
 
 using namespace psi;
 
diff --git a/psi4/src/psi4/occ/arrays.cc b/psi4/src/psi4/occ/arrays.cc
index c63ef4fb124..85b621ccdc5 100644
--- a/psi4/src/psi4/occ/arrays.cc
+++ b/psi4/src/psi4/occ/arrays.cc
@@ -34,7 +34,7 @@
 #include "psi4/libpsi4util/exception.h"
 #include "psi4/libpsi4util/PsiOutStream.h"
 
-#include <stdio.h>
+#include <cstdio>
 #include <cmath>
 
 using namespace psi;
diff --git a/psi4/src/psi4/optking/bend.cc b/psi4/src/psi4/optking/bend.cc
index aa23d5d7e40..d457ebcd390 100644
--- a/psi4/src/psi4/optking/bend.cc
+++ b/psi4/src/psi4/optking/bend.cc
@@ -33,7 +33,7 @@
 #include "bend.h"
 
 #include <sstream>
-#include <math.h>
+#include <cmath>
 
 #include "v3d.h"
 #include "psi4/optking/physconst.h"
diff --git a/psi4/src/psi4/optking/io.h b/psi4/src/psi4/optking/io.h
index 0455204dffc..df21c5be763 100644
--- a/psi4/src/psi4/optking/io.h
+++ b/psi4/src/psi4/optking/io.h
@@ -36,7 +36,7 @@
 
 #include "package.h"
 
-#include <stddef.h>
+#include <cstddef>
 
 namespace opt {