diff --git a/Makefile b/Makefile
index 7986ebb..e214557 100644
--- a/Makefile
+++ b/Makefile
@@ -10,6 +10,7 @@ Q         ?= @
 include $(MAKE_DIR)/config.mk
 include $(MAKE_DIR)/include_$(TAG).mk
 include $(MAKE_DIR)/include_LIKWID.mk
+include $(MAKE_DIR)/include_GROMACS.mk
 INCLUDES  += -I./$(SRC_DIR)/includes
 
 ifeq ($(strip $(DATA_LAYOUT)),AOS)
@@ -52,6 +53,10 @@ ifeq ($(strip $(COMPUTE_STATS)),true)
     DEFINES += -DCOMPUTE_STATS
 endif
 
+ifeq ($(strip $(XTC_OUTPUT)),true)
+    DEFINES += -DXTC_OUTPUT
+endif
+
 ifeq ($(strip $(USE_REFERENCE_VERSION)),true)
     DEFINES += -DUSE_REFERENCE_VERSION
 endif
@@ -64,6 +69,10 @@ ifneq ($(VECTOR_WIDTH),)
     DEFINES += -DVECTOR_WIDTH=$(VECTOR_WIDTH)
 endif
 
+ifeq ($(strip $(NO_AVX2)),true)
+    DEFINES += -DNO_AVX2
+endif
+
 VPATH     = $(SRC_DIR) $(ASM_DIR)
 ASM       = $(patsubst $(SRC_DIR)/%.c, $(BUILD_DIR)/%.s,$(wildcard $(SRC_DIR)/*.c))
 OVERWRITE:= $(patsubst $(ASM_DIR)/%-new.s, $(BUILD_DIR)/%.o,$(wildcard $(ASM_DIR)/*-new.s))
diff --git a/config.mk b/config.mk
index 62206d8..6a27e04 100644
--- a/config.mk
+++ b/config.mk
@@ -1,9 +1,9 @@
 # Compiler tag (GCC/CLANG/ICC)
 TAG ?= ICC
 # Optimization scheme (lammps/gromacs/clusters_per_bin)
-OPT_SCHEME = gromacs
+OPT_SCHEME ?= gromacs
 # Enable likwid (true or false)
-ENABLE_LIKWID ?= false
+ENABLE_LIKWID ?= true
 # SP or DP
 DATA_TYPE ?= DP
 # AOS or SOA
@@ -24,7 +24,9 @@ MEM_TRACER ?= false
 # Trace indexes and distances for gather-md (true or false)
 INDEX_TRACER ?= false
 # Vector width (elements) for index and distance tracer
-VECTOR_WIDTH ?= 8
+VECTOR_WIDTH ?= 4
+# When vector width is 4 but AVX2 is not supported (AVX only), set this to true
+NO_AVX2 ?= true
 # Compute statistics
 COMPUTE_STATS ?= true
 
@@ -33,6 +35,8 @@ COMPUTE_STATS ?= true
 CLUSTER_LAYOUT ?= SOA
 # Use reference version
 USE_REFERENCE_VERSION ?= false
+# Enable XTC output
+XTC_OUTPUT ?= false
 
 #Feature options
 OPTIONS =  -DALIGNMENT=64
diff --git a/gromacs/includes/parameter.h b/gromacs/includes/parameter.h
index 84a0cdb..c5a03a5 100644
--- a/gromacs/includes/parameter.h
+++ b/gromacs/includes/parameter.h
@@ -33,6 +33,7 @@ typedef struct {
     int force_field;
     char* input_file;
     char* vtk_file;
+    char *xtc_file;
     MD_FLOAT epsilon;
     MD_FLOAT sigma6;
     MD_FLOAT temp;
@@ -41,8 +42,10 @@ typedef struct {
     int ntypes;
     int ntimes;
     int nstat;
-    int every;
+    int reneigh_every;
     int prune_every;
+    int x_out_every;
+    int v_out_every;
     MD_FLOAT dt;
     MD_FLOAT dtforce;
     MD_FLOAT cutforce;
diff --git a/gromacs/includes/simd.h b/gromacs/includes/simd.h
index 9e1f443..ad86e7b 100644
--- a/gromacs/includes/simd.h
+++ b/gromacs/includes/simd.h
@@ -41,10 +41,10 @@ static inline MD_SIMD_FLOAT simd_mul(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return
 static inline MD_SIMD_FLOAT simd_fma(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_FLOAT c) { return _mm512_fmadd_pd(a, b, c); }
 static inline MD_SIMD_FLOAT simd_reciprocal(MD_SIMD_FLOAT a) { return _mm512_rcp14_pd(a); }
 static inline MD_SIMD_FLOAT simd_masked_add(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_MASK m) { return _mm512_mask_add_pd(a, m, a, b); }
-static inline MD_SIMD_MASK simd_mask_from_u32(unsigned int a) { return _cvtu32_mask8(a); }
-static inline MD_SIMD_MASK simd_mask_to_u32(unsigned int a) { return _cvtmask8_u32(a); }
 static inline MD_SIMD_MASK simd_mask_and(MD_SIMD_MASK a, MD_SIMD_MASK b) { return _kand_mask8(a, b); }
 static inline MD_SIMD_MASK simd_mask_cond_lt(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm512_cmp_pd_mask(a, b, _CMP_LT_OQ); }
+static inline MD_SIMD_MASK simd_mask_from_u32(unsigned int a) { return _cvtu32_mask8(a); }
+static inline unsigned int simd_mask_to_u32(MD_SIMD_MASK a) { return _cvtmask8_u32(a); }
 
 static MD_SIMD_FLOAT simd_load2(MD_FLOAT *c0, MD_FLOAT *c1, int d) {
     MD_SIMD_FLOAT x;
@@ -64,39 +64,55 @@ static inline MD_FLOAT simd_horizontal_sum(MD_SIMD_FLOAT a) {
     MD_SIMD_FLOAT x = _mm512_add_pd(a, _mm512_shuffle_f64x2(a, a, 0xee));
     x = _mm512_add_pd(x, _mm512_shuffle_f64x2(x, x, 0x11));
     x = _mm512_add_pd(x, _mm512_permute_pd(x, 0x01));
-    return *((double *) &x);
+    return *((MD_FLOAT *) &x);
 }
 
-#else // AVX2
+#else // AVX or AVX2
 
 #define MD_SIMD_FLOAT       __m256d
+
+#ifdef NO_AVX2
+#define MD_SIMD_MASK        __m256d
+#else
 #define MD_SIMD_MASK        __mmask8
+#endif
 
 static inline MD_SIMD_FLOAT simd_broadcast(double scalar) { return _mm256_set1_pd(scalar); }
 static inline MD_SIMD_FLOAT simd_zero() { return _mm256_set1_pd(0.0); }
 static inline MD_SIMD_FLOAT simd_add(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm256_add_pd(a, b); }
 static inline MD_SIMD_FLOAT simd_sub(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm256_sub_pd(a, b); }
 static inline MD_SIMD_FLOAT simd_mul(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm256_mul_pd(a, b); }
-static inline MD_SIMD_FLOAT simd_fma(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_FLOAT c) { return _mm256_fmadd_pd(a, b, c); }
-static inline MD_SIMD_FLOAT simd_reciprocal(MD_SIMD_FLOAT a) { return _mm256_rcp14_pd(a); }
-static inline MD_SIMD_FLOAT simd_masked_add(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_MASK m) { return _mm256_mask_add_pd(a, m, a, b); }
-static inline MD_SIMD_MASK simd_mask_from_u32(unsigned int a) { return _cvtu32_mask8(a); }
-static inline MD_SIMD_MASK simd_mask_to_u32(unsigned int a) { return _cvtmask8_u32(a); }
-static inline MD_SIMD_MASK simd_mask_and(MD_SIMD_MASK a, MD_SIMD_MASK b) { return _kand_mask8(a, b); }
-static inline MD_SIMD_MASK simd_mask_cond_lt(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm256_cmp_pd_mask(a, b, _CMP_LT_OQ); }
 
-static MD_SIMD_FLOAT simd_load(MD_FLOAT *c0, int d) {
-    MD_SIMD_FLOAT x;
-#ifdef CLUSTER_AOS
-    __m128i aos_gather_vindex = _mm128_set_epi32(9, 6, 3, 0);
-    __m128i vindex = _mm128_add_epi32(aos_gather_vindex, _mm128_set1_epi32(d));
-    x = _mm256_i32gather_pd(c0, vindex, sizeof(double));
-#else
-    x = _mm256_load_pd(&c0[d * CLUSTER_DIM_M]);
-#endif
-    return x;
+#ifdef NO_AVX2
+static inline MD_SIMD_FLOAT simd_reciprocal(MD_SIMD_FLOAT a) { return _mm256_cvtps_pd(_mm_rcp_ps(_mm256_cvtpd_ps(a))); }
+static inline MD_SIMD_FLOAT simd_fma(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_FLOAT c) { return simd_add(simd_mul(a, b), c); }
+static inline MD_SIMD_FLOAT simd_masked_add(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_MASK m) { return simd_add(a, _mm256_and_pd(b, m)); }
+static inline MD_SIMD_MASK simd_mask_cond_lt(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm256_cmp_pd(a, b, _CMP_LT_OQ); }
+static inline MD_SIMD_MASK simd_mask_and(MD_SIMD_MASK a, MD_SIMD_MASK b) { return _mm256_and_pd(a, b); }
+// TODO: Initialize all diagonal cases and just select the proper one (all bits set or diagonal) based on cond0
+static inline MD_SIMD_MASK simd_mask_from_u32(unsigned int a) {
+    const unsigned long long int all = 0xFFFFFFFFFFFFFFFF;
+    const unsigned long long int none = 0x0;
+    return _mm256_castsi256_pd(_mm256_set_epi64x((a & 0x8) ? all : none, (a & 0x4) ? all : none, (a & 0x2) ? all : none, (a & 0x1) ? all : none));
 }
-
+// TODO: Implement this, althrough it is just required for debugging
+static inline int simd_mask_to_u32(MD_SIMD_MASK a) { return 0; }
+static inline MD_FLOAT simd_horizontal_sum(MD_SIMD_FLOAT a) {
+    __m128d a0, a1;
+    a = _mm256_add_pd(a, _mm256_permute_pd(a, 0b0101));
+    a0 = _mm256_castpd256_pd128(a);
+    a1 = _mm256_extractf128_pd(a, 0x1);
+    a0 = _mm_add_sd(a0, a1);
+    return *((MD_FLOAT *) &a0);
+}
+#else
+static inline MD_SIMD_FLOAT simd_reciprocal(MD_SIMD_FLOAT a) { return _mm256_rcp14_pd(a); }
+static inline MD_SIMD_FLOAT simd_fma(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_FLOAT c) { return _mm256_fmadd_pd(a, b, c); }
+static inline MD_SIMD_FLOAT simd_masked_add(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b, MD_SIMD_MASK m) { return _mm256_mask_add_pd(a, m, a, b); }
+static inline MD_SIMD_MASK simd_mask_cond_lt(MD_SIMD_FLOAT a, MD_SIMD_FLOAT b) { return _mm256_cmp_pd_mask(a, b, _CMP_LT_OQ); }
+static inline MD_SIMD_MASK simd_mask_and(MD_SIMD_MASK a, MD_SIMD_MASK b) { return _kand_mask8(a, b); }
+static inline MD_SIMD_MASK simd_mask_from_u32(unsigned int a) { return _cvtu32_mask8(a); }
+static inline unsigned int simd_mask_to_u32(MD_SIMD_MASK a) { return _cvtmask8_u32(a); }
 static inline MD_FLOAT simd_horizontal_sum(MD_SIMD_FLOAT a) {
     __m128d a0, a1;
     // test with shuffle & add as an alternative to hadd later
@@ -104,7 +120,23 @@ static inline MD_FLOAT simd_horizontal_sum(MD_SIMD_FLOAT a) {
     a0 = _mm256_castpd256_pd128(a);
     a1 = _mm256_extractf128_pd(a, 0x1);
     a0 = _mm_add_sd(a0, a1);
-    return *((double *) &a0);
+    return *((MD_FLOAT *) &a0);
+}
+#endif
+
+static MD_SIMD_FLOAT simd_load(MD_FLOAT *c0, int d) {
+    MD_SIMD_FLOAT x;
+#ifdef CLUSTER_AOS
+    #ifdef NO_AVX2
+    #error "Not possible to use AoS cluster layout without AVX2 support!"
+    #endif
+    __m128i aos_gather_vindex = _mm128_set_epi32(9, 6, 3, 0);
+    __m128i vindex = _mm128_add_epi32(aos_gather_vindex, _mm128_set1_epi32(d));
+    x = _mm256_i32gather_pd(c0, vindex, sizeof(double));
+#else
+    x = _mm256_load_pd(&c0[d * CLUSTER_DIM_M]);
+#endif
+    return x;
 }
 
 #endif
diff --git a/gromacs/includes/xtc.h b/gromacs/includes/xtc.h
new file mode 100644
index 0000000..96ecfc6
--- /dev/null
+++ b/gromacs/includes/xtc.h
@@ -0,0 +1,37 @@
+/*
+ * =======================================================================================
+ *
+ *   Author:   Jan Eitzinger (je), jan.eitzinger@fau.de
+ *   Copyright (c) 2020 RRZE, University Erlangen-Nuremberg
+ *
+ *   This file is part of MD-Bench.
+ *
+ *   MD-Bench is free software: you can redistribute it and/or modify it
+ *   under the terms of the GNU Lesser General Public License as published
+ *   by the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   MD-Bench is distributed in the hope that it will be useful, but WITHOUT ANY
+ *   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ *   PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+ *   details.
+ *
+ *   You should have received a copy of the GNU Lesser General Public License along
+ *   with MD-Bench.  If not, see <https://www.gnu.org/licenses/>.
+ * =======================================================================================
+ */
+#include <atom.h>
+
+#ifndef __XTC_H_
+#define __XTC_H_
+
+#ifdef XTC_OUTPUT
+void xtc_init(const char *, Atom*, int);
+void xtc_write(Atom*, int, int, int);
+void xtc_end();
+#else
+#define xtc_init(a,b,c)
+#define xtc_write(a,b,c,d)
+#define xtc_end()
+#endif
+#endif
diff --git a/gromacs/main.c b/gromacs/main.c
index 2c5f013..773ee09 100644
--- a/gromacs/main.c
+++ b/gromacs/main.c
@@ -41,6 +41,7 @@
 #include <timers.h>
 #include <eam.h>
 #include <vtk.h>
+#include <xtc.h>
 #include <util.h>
 
 #define HLINE "----------------------------------------------------------------------------\n"
@@ -58,6 +59,7 @@ extern double computeForceEam(Eam*, Parameter*, Atom*, Neighbor*, Stats*);
 void init(Parameter *param) {
     param->input_file = NULL;
     param->vtk_file = NULL;
+    param->xtc_file = NULL;
     param->force_field = FF_LJ;
     param->epsilon = 1.0;
     param->sigma6 = 1.0;
@@ -75,8 +77,10 @@ void init(Parameter *param) {
     param->nstat = 100;
     param->mass = 1.0;
     param->dtforce = 0.5 * param->dt;
-    param->every = 20;
+    param->reneigh_every = 20;
     param->prune_every = 1000;
+    param->x_out_every = 20;
+    param->v_out_every = 5;
     param->proc_freq = 2.4;
 }
 
@@ -241,6 +245,15 @@ int main(int argc, char** argv) {
             param.vtk_file = strdup(argv[++i]);
             continue;
         }
+        if((strcmp(argv[i], "--xtc") == 0)) {
+            #ifndef XTC_OUTPUT
+            fprintf(stderr, "XTC not available, set XTC_OUTPUT option in config.mk file and recompile MD-Bench!");
+            exit(-1);
+            #else
+            param.xtc_file = strdup(argv[++i]);
+            #endif
+            continue;
+        }
         if((strcmp(argv[i], "-h") == 0) || (strcmp(argv[i], "--help") == 0)) {
             printf("MD Bench: A minimalistic re-implementation of miniMD\n");
             printf(HLINE);
@@ -253,6 +266,7 @@ int main(int argc, char** argv) {
             printf("-s / --skin <real>:   set skin (verlet buffer)\n");
             printf("--freq <real>:        processor frequency (GHz)\n");
             printf("--vtk <string>:       VTK file for visualization\n");
+            printf("--xtc <string>:       XTC file for visualization\n");
             printf(HLINE);
             exit(EXIT_SUCCESS);
         }
@@ -277,10 +291,14 @@ int main(int argc, char** argv) {
         write_data_to_vtk_file(param.vtk_file, &atom, 0);
     }
 
+    if(param.xtc_file != NULL) {
+        xtc_init(param.xtc_file, &atom, 0);
+    }
+
     for(int n = 0; n < param.ntimes; n++) {
         initialIntegrate(&param, &atom);
 
-        if((n + 1) % param.every) {
+        if((n + 1) % param.reneigh_every) {
             if(!((n + 1) % param.prune_every)) {
                 pruneNeighbor(&param, &atom, &neighbor);
             }
@@ -306,14 +324,26 @@ int main(int argc, char** argv) {
             computeThermo(n + 1, &param, &atom);
         }
 
-        if(param.vtk_file != NULL) {
-            write_data_to_vtk_file(param.vtk_file, &atom, n + 1);
+        int write_pos = !((n + 1) % param.x_out_every);
+        int write_vel = !((n + 1) % param.v_out_every);
+        if(write_pos || write_vel) {
+            if(param.vtk_file != NULL) {
+                write_data_to_vtk_file(param.vtk_file, &atom, n + 1);
+            }
+
+            if(param.xtc_file != NULL) {
+                xtc_write(&atom, n + 1, write_pos, write_vel);
+            }
         }
     }
 
     timer[TOTAL] = getTimeStamp() - timer[TOTAL];
     computeThermo(-1, &param, &atom);
 
+    if(param.xtc_file != NULL) {
+        xtc_end();
+    }
+
     printf(HLINE);
     printf("Force field: %s\n", ff2str(param.force_field));
     printf("Data layout for positions: %s\n", POS_DATA_LAYOUT);
diff --git a/gromacs/xtc.c b/gromacs/xtc.c
new file mode 100644
index 0000000..d381f40
--- /dev/null
+++ b/gromacs/xtc.c
@@ -0,0 +1,71 @@
+/*
+ * =======================================================================================
+ *
+ *   Author:   Jan Eitzinger (je), jan.eitzinger@fau.de
+ *   Copyright (c) 2020 RRZE, University Erlangen-Nuremberg
+ *
+ *   This file is part of MD-Bench.
+ *
+ *   MD-Bench is free software: you can redistribute it and/or modify it
+ *   under the terms of the GNU Lesser General Public License as published
+ *   by the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   MD-Bench is distributed in the hope that it will be useful, but WITHOUT ANY
+ *   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ *   PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
+ *   details.
+ *
+ *   You should have received a copy of the GNU Lesser General Public License along
+ *   with MD-Bench.  If not, see <https://www.gnu.org/licenses/>.
+ * =======================================================================================
+ */
+#include <stdlib.h>
+//---
+#include <atom.h>
+#include <allocate.h>
+#include <xtc.h>
+
+#ifdef XTC_OUTPUT
+#include <gromacs/fileio/xtcio.h>
+
+static struct t_fileio *xtc_file = NULL;
+static rvec *x_buf = NULL;
+static rvec basis[3];
+
+void xtc_init(const char *filename, Atom *atom, int timestep) {
+    basis[0][XX] = 1.0;
+    basis[0][YY] = 0.0;
+    basis[0][ZZ] = 0.0;
+    basis[1][XX] = 0.0;
+    basis[1][YY] = 1.0;
+    basis[1][ZZ] = 0.0;
+    basis[2][XX] = 0.0;
+    basis[2][YY] = 0.0;
+    basis[2][ZZ] = 1.0;
+
+    xtc_file = open_xtc(filename, "w");
+    x_buf = (rvec *) allocate(ALIGNMENT, sizeof(rvec) * (atom->Nlocal + 1));
+    xtc_write(atom, timestep, 1, 1);
+}
+
+void xtc_write(Atom *atom, int timestep, int write_pos, int write_vel) {
+    int i = 0;
+    for(int ci = 0; ci < atom->Nclusters_local; ++ci) {
+        MD_FLOAT *cptr = cluster_pos_ptr(ci);
+        for(int cii = 0; cii < atom->clusters[ci].natoms; ++cii) {
+            x_buf[i][XX] = cluster_x(cptr, cii);
+            x_buf[i][YY] = cluster_y(cptr, cii);
+            x_buf[i][ZZ] = cluster_z(cptr, cii);
+            i++;
+        }
+    }
+
+    write_xtc(xtc_file, atom->Nlocal, timestep, 0.0, (const rvec *) basis, (const rvec *) x_buf, 1000);
+}
+
+void xtc_end() {
+    free(x_buf);
+    close_xtc(xtc_file);
+}
+#endif
diff --git a/include_GROMACS.mk b/include_GROMACS.mk
new file mode 100644
index 0000000..d91198d
--- /dev/null
+++ b/include_GROMACS.mk
@@ -0,0 +1,11 @@
+GROMACS_PATH=/apps/Gromacs/2018.1-mkl
+GROMACS_INC ?= -I${GROMACS_PATH}/include
+GROMACS_DEFINES ?=
+GROMACS_LIB ?= -L${GROMACS_PATH}/lib64
+
+ifeq ($(strip $(XTC_OUTPUT)),true)
+INCLUDES += ${GROMACS_INC}
+DEFINES +=  ${GROMACS_DEFINES}
+LIBS += -lgromacs
+LFLAGS += ${GROMACS_LIB}
+endif